2.4-only: remove 2.3.9/2.3.10 trivia

Merge r1588747 from trunk:

expr=value updates:
 update RequestHeader syntax, 
 add compat to Header and RequestHeader




git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1588748 13f79535-47bb-0310-9956-ffa450edef68