Add mod_deflate build support, along with module enablement options

"a" and "i" which are ignored with a warning if a prerequisite
is not found.

Fix the mod_ssl build to use the same mechanism, and to use
enablement option "i" so that it is installed but not loaded
if its prereq (OpenSSL) is available.

Fix a few messaging buglets.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1518041 13f79535-47bb-0310-9956-ffa450edef68