Merge r611475 from trunk:

Don't add bogus duplicate Content-Language header entries.
PR 11035

Submitted by: niq
Reviewed by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.2.x@631363 13f79535-47bb-0310-9956-ffa450edef68