Merge the <If> sections in a separate step ap_if_walk, after ap_location_walk.

This makes <If> apply to all requests, not only to file base requests and
it allows to use <If> inside <Directory>, <Location>, and <Files> sections.

The merging of <If> sections always happens after the merging of <Location>
sections, even if the <If> section is embedded inside a <Directory> or
<Files> section.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1059867 13f79535-47bb-0310-9956-ffa450edef68