Deploy test2.war
Hit url:
http://localhost:8080/test2/test3.jsp

This change happened after moving from EAP 6.4 CP5 to CP6 where jstl had some bugs fixed.

test3.jsp:
------------
<c:import var="xslStylesheet" url="/xsl/ident/style3.xsl" charEncoding="UTF-8" />
<c:import url="http://localhost:8080/test2/test.xml" var="doc"/>
<x:transform xml="${doc}" xslt="${xslStylesheet}" xsltSystemId="/xsl/">
</x:transform> 

style3.xsl
---------------
<?xml version="1.0"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
                xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
                version="1.0">

    <xsl:import href="parent.xsl"/>
...

17:41:17,145 ERROR [org.apache.catalina.core.ContainerBase.[jboss.web].[default-host].[/test2].[jsp]] (http-127.0.0.1:8080-1) JBWEB000236: Servlet.service() for servlet jsp threw exception: java.net.MalformedURLException: unknown protocol: jstl
	at java.net.URL.<init>(URL.java:592) [rt.jar:1.7.0_51]
	at java.net.URL.<init>(URL.java:482) [rt.jar:1.7.0_51]
	at java.net.URL.<init>(URL.java:431) [rt.jar:1.7.0_51]
	at org.apache.xerces.impl.XMLEntityManager.setupCurrentEntity(XMLEntityManager.java:959)
	at org.apache.xerces.impl.XMLVersionDetector.determineDocVersion(XMLVersionDetector.java:143)
	at org.apache.xerces.parsers.XML11Configuration.parse(XML11Configuration.java:802)
	at org.apache.xerces.parsers.XML11Configuration.parse(XML11Configuration.java:768)
	at org.apache.xerces.parsers.XMLParser.parse(XMLParser.java:108)
	at org.apache.xerces.parsers.AbstractSAXParser.parse(AbstractSAXParser.java:1196)
	at org.apache.xerces.jaxp.SAXParserImpl$JAXPSAXParser.parse(SAXParserImpl.java:555)
	at org.apache.xalan.processor.ProcessorInclude.parse(ProcessorInclude.java:312)
	at org.apache.xalan.processor.ProcessorInclude.startElement(ProcessorInclude.java:158)
	at org.apache.xalan.processor.StylesheetHandler.startElement(StylesheetHandler.java:626)
	at org.apache.xerces.parsers.AbstractSAXParser.startElement(AbstractSAXParser.java:496)
	at org.apache.xerces.parsers.AbstractXMLDocumentParser.emptyElement(AbstractXMLDocumentParser.java:180)
	at org.apache.xerces.impl.XMLNSDocumentScannerImpl.scanStartElement(XMLNSDocumentScannerImpl.java:275)
	at org.apache.xerces.impl.XMLDocumentFragmentScannerImpl$FragmentContentDispatcher.dispatch(XMLDocumentFragmentScannerImpl.java:1653)
	at org.apache.xerces.impl.XMLDocumentFragmentScannerImpl.scanDocument(XMLDocumentFragmentScannerImpl.java:324)
	at org.apache.xerces.parsers.XML11Configuration.parse(XML11Configuration.java:845)
	at org.apache.xerces.parsers.XML11Configuration.parse(XML11Configuration.java:768)
	at org.apache.xerces.parsers.XMLParser.parse(XMLParser.java:108)
	at org.apache.xerces.parsers.AbstractSAXParser.parse(AbstractSAXParser.java:1196)
	at org.apache.xerces.jaxp.SAXParserImpl$JAXPSAXParser.parse(SAXParserImpl.java:555)
	at org.apache.xalan.processor.TransformerFactoryImpl.newTemplates(TransformerFactoryImpl.java:926)
	at org.apache.xalan.processor.TransformerFactoryImpl.newTransformer(TransformerFactoryImpl.java:780)
	at __redirected.__TransformerFactory.newTransformer(__TransformerFactory.java:132) [jboss-modules.jar:1.3.7.Final-redhat-1]
	at org.apache.taglibs.standard.util.XmlUtil.newTransformer(XmlUtil.java:195) [jboss-jstl-api_1.2_spec-1.0.9.Final-redhat-1.jar:1.0.9.Final]
	at org.apache.taglibs.standard.tag.common.xml.TransformSupport.doStartTag(TransformSupport.java:124) [jboss-jstl-api_1.2_spec-1.0.9.Final-redhat-1.jar:1.0.9.Final]
	at org.apache.jsp.test3_jsp._jspx_meth_x_005ftransform_005f0(test3_jsp.java:230)
	at org.apache.jsp.test3_jsp._jspService(test3_jsp.java:91)
	at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:69) [jbossweb-7.5.15.Final-redhat-1.jar:7.5.15.Final-redhat-1]
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:847) [jboss-servlet-api_3.0_spec-1.0.2.Final-redhat-2.jar:1.0.2.Final-redhat-2]
	at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:365) [jbossweb-7.5.15.Final-redhat-1.jar:7.5.15.Final-redhat-1]
	at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:309) [jbossweb-7.5.15.Final-redhat-1.jar:7.5.15.Final-redhat-1]
	at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:242) [jbossweb-7.5.15.Final-redhat-1.jar:7.5.15.Final-redhat-1]
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:847) [jboss-servlet-api_3.0_spec-1.0.2.Final-redhat-2.jar:1.0.2.Final-redhat-2]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:295) [jbossweb-7.5.15.Final-redhat-1.jar:7.5.15.Final-redhat-1]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:214) [jbossweb-7.5.15.Final-redhat-1.jar:7.5.15.Final-redhat-1]
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:231) [jbossweb-7.5.15.Final-redhat-1.jar:7.5.15.Final-redhat-1]
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:149) [jbossweb-7.5.15.Final-redhat-1.jar:7.5.15.Final-redhat-1]
	at org.jboss.as.web.security.SecurityContextAssociationValve.invoke(SecurityContextAssociationValve.java:169) [jboss-as-web-7.5.7.Final-redhat-2.jar:7.5.7.Final-redhat-2]
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:150) [jbossweb-7.5.15.Final-redhat-1.jar:7.5.15.Final-redhat-1]
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:97) [jbossweb-7.5.15.Final-redhat-1.jar:7.5.15.Final-redhat-1]
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:102) [jbossweb-7.5.15.Final-redhat-1.jar:7.5.15.Final-redhat-1]
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:344) [jbossweb-7.5.15.Final-redhat-1.jar:7.5.15.Final-redhat-1]
	at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:854) [jbossweb-7.5.15.Final-redhat-1.jar:7.5.15.Final-redhat-1]
	at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:654) [jbossweb-7.5.15.Final-redhat-1.jar:7.5.15.Final-redhat-1]
	at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:926) [jbossweb-7.5.15.Final-redhat-1.jar:7.5.15.Final-redhat-1]
	at java.lang.Thread.run(Thread.java:744) [rt.jar:1.7.0_51]