Expand file text comparison to cover arrays of sources

[kpaulisse]

This PR expands the "compare file text" option, which back-fills the actual text of a file into the catalog so that comparison can occur. The change here enables arrays as well:

file { '/tmp/some-file.txt':
  source => ['puppet:///modules/test/some-file.txt.special', 'puppet:///modules/test/some-file.txt'], 
}

Fixes #150