Change the default install location for Apache modules to $prefix/libexec
instead of the installed Apache's modules directory, which can easily be
outside $prefix. This also changes the default of the configure option
--with-apache-libexecdir from "yes" to "no".

* build/ac-macros/apache.m4: Set default value of APACHE_LIBEXECDIR to "no",
   update option value processing and update the docstring of the
   --with-apache-libexecdir configure option.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1469862 13f79535-47bb-0310-9956-ffa450edef68