Make ap_check_cmd_context() treat <If> sections like <File> sections.

This is necessary to properly disallow directives that don't work in
<If>.
    
A separate NOT_IN_IF flag may be nicer, but would create much more
hassle when being backported to 2.4.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1406495 13f79535-47bb-0310-9956-ffa450edef68