Apache_allowed_from and Scientific Linux support

I tried to make this two separate pull requests, but the second was integrated into the first, sorry.

* Added apache_allowed_from parameter for default template
Interestingly enough, I don't seem need anything specific for the puppetlabs/apache module... only the following includes:
    apache
    apache::mod::php
    apache::ssl

* Added support for Scientific Linux
It's very much like Fedora

* Changed location of nagios server pidfile to /var/run
I changed the pidfile in nagios.cfg from /var/run/nagios to /var/run, that's more generic and targets all OS versions (SL as well).
Since it's a "local mod" I did not want to make it part of the pull request, but it came with the push, feel free to reject it if you don't like it.