apache-httpd: Dynamically load MPM module in v2.4.

Now, MPMs can be loaded at runtime and it's no longer required to compile in one
of the MPM modules statically. So, if version is >= 2.4, load the MPM module
corresponding to the multiProcessingModule value of the service module.

For details, please see: http://httpd.apache.org/docs/2.4/mpm.html



Signed-off-by: aszlig <aszlig@redmoonstudios.org>