Implement mpm_itk on Debian

added what needed to have mpm-itk working on Debian based systems.
Fix failing system spec test
fix failing system specs reported in #347
Merge pull request #347 from blkperl/fix_system_test

Fix failing system spec test
Fix apache::default_mods loading

PR #314 was merged without tests and consequently had bugs. This moves
the `apache::default_mods::load` defined resource into
`manifests/default_mods/load.pp` and adds the missing `mods` parameter
to the `apache::default_mods` class. Also lots of tests are added.
Merge pull request #348 from hunner/fix_314

Fix apache::default_mods loading
Merge pull request #304 from kumy/itk

Add stuff to use ITK on Debian
Remove default <proxy *> block

This is a horrible and generally useless default. Most people do *not*
use apache httpd as Forward proxy, and those who do, should explicitly
set an allow. That this is exactly what our new, and backward
compatible proxy config does, and allows, while widly simplifying the
reverse proxy configurations.

We add a test case for new proxy configuration to make sure this is
actually the case, and also fix a test case from a previious commit.