Description of problem:
CVE-2008-3790 patch has a regression that parsing XML causes unexpected error.

See 
Debian -> http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=502535
Ubuntu -> https://bugs.launchpad.net/ubuntu/+source/ruby1.8/+bug/291893

Version-Release number of selected component (if applicable):
$ rpm -q ruby
ruby-1.8.6.287-3.fc11.x86_64

How reproducible:


Steps to Reproduce:
$ ruby -r rexml/document -r open-uri -e 'REXML::Document.new(URI.parse("http://github.com/bioruby/bioruby/tree/master%2Ftest%2Fdata%2Fblast%2Fb0002.faa.m7?raw=true").read).root.each_element_with_text { |e| p e.name }'

  
Actual results:
"BlastOutput_program"
"BlastOutput_version"
/usr/lib/ruby/1.8/rexml/entity.rb:76:in `unnormalized': undefined method `record_entity_expansion' for nil:NilClass (NoMethodError)
        from /usr/lib/ruby/1.8/rexml/doctype.rb:135:in `entity'
        from /usr/lib/ruby/1.8/rexml/text.rb:325:in `unnormalize'
        from /usr/lib/ruby/1.8/rexml/text.rb:323:in `each'
        from /usr/lib/ruby/1.8/rexml/text.rb:323:in `unnormalize'
        from /usr/lib/ruby/1.8/rexml/text.rb:174:in `value'
        from /usr/lib/ruby/1.8/rexml/element.rb:452:in `text'
        from /usr/lib/ruby/1.8/rexml/element.rb:433:in `has_text?'
        from /usr/lib/ruby/1.8/rexml/element.rb:384:in `each_element_with_text'
        from /usr/lib/ruby/1.8/rexml/element.rb:709:in `call'
        from /usr/lib/ruby/1.8/rexml/element.rb:709:in `each_with_something'
        from /usr/lib/ruby/1.8/rexml/element.rb:891:in `each'
        from /usr/lib/ruby/1.8/rexml/xpath.rb:53:in `each'
        from /usr/lib/ruby/1.8/rexml/element.rb:891:in `each'
        from /usr/lib/ruby/1.8/rexml/element.rb:708:in `each_with_something'
        from /usr/lib/ruby/1.8/rexml/element.rb:388:in `each_element_with_text'
        from -e:1


Expected results:
No error

Additional info:
Patch is attached on Debian bug (http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=502535)