ruby_version should allow fully qualified strings including gemset

Pull request 60 / 790bdab solved a longstanding problem we had with passenger dependency order, but it broke the ability to use a fully qualified RVM ruby_version string like "ruby-1.9.3-p392@mygemset" with rvm::passenger::apache.

lib/puppet/type/rvm_gem.rb describes the ruby_version string as:
```
The ruby version to use.  This should be the fully qualified RVM string
(including gemset if applicable).  For example: 'ruby-1.9.2-p136@mygemset'
```
This pull request restores the ability to pass a fully qualified ruby_version string to the rvm::passenger::apache parametrized class.

Cheers and thanks to @blt04 for the module and @angusscown for the dependency fix!