Description of problem:
If httpd is configured with ProxyPass to backend server, and this server returns http code 1100, httpd in some cases returns 1100 and original messages, in other cases status 502 Proxy Error.

In both cases, this error is logged:
[Wed Apr 20 15:18:08.451756 2016] [proxy_http:error] [pid 17992] (20014)Internal error: [client ::1:50750] AH01102: error reading status line from remote server localhost:8123
[Wed Apr 20 15:18:08.451835 2016] [proxy:error] [pid 17992] [client ::1:50750] AH00898: Error reading from remote server returned by /fake-server

Version-Release number of selected component (if applicable):
httpd24-httpd-2.4.18-10

How reproducible:
not sure, maybe dependent on environment

Steps to Reproduce:
1. configure httpd to use backend server (ProxyPass /path http://localhost:8123)
2. run fake server on 8123 port, which returns this message:
"""
HTTP/1.1 1100
Content-Length: 5
Server: fake

abcde
"""
3. systemctl start httpd24-httpd
4. download page, check header

Actual results:
HTTP/1.1 1100 
Content-Length: 5
Server: fake

Expected results:
HTTP/1.1 502 Proxy Error
Date: Sun, 24 Apr 2016 19:36:11 GMT
Server: Apache/2.4.18 (Red Hat) mod_auth_kerb/5.4
Content-Length: 405
Content-Type: text/html; charset=iso-8859-1

Additional info: