Improved version selection, prep for 2.1.0 release

[sambauers]

Drys up the secure version checks as well by using a new puppet custom function.

[sambauers]

This replaces #81 (except for the version changes to the APC extension)

[sambauers]

@mattheath I think this is important. It may fix some other spurious issues that people are reporting about duplicate resources.

[sambauers]

#71 may be related to this. @outrunthewolf was specifying '5.3' as the version on PHP, which would have been rewritten to 5.4.something, and possibly dying due to duplicate on the FPM resource later on.

[sambauers]

I'm not using Boxen where I am anymore. Just thought I would bump this with the latest PHP versions and updates to code to handle them.

[sambauers]

@jacobbednarz I've updated this PR against the latest master. I think it should be merged and tagged with a 2.1.0 release. I've updated the change log to reflect this as well. Could probably do with a second set of eyes to make sure it integrates with other people's existing Boxen setup.