proxy/ajp_header.c: Fixed header token string comparisons

Matching of header tokens failed to include the trailing NIL byte
and could misinterpret a longer header token for a shorter.
Additionally, a "Content-Type" comparison was made case insensitive.
Based on trunk rev. 571219,571232


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.2.x@571409 13f79535-47bb-0310-9956-ffa450edef68