Windows-compatibility: Calling LAME through the command line

Some Windows-incompatibilities have crept into the Islandora codebase ([additional background can be found here](https://groups.google.com/d/msg/islandora/0MAhLDjbago/9knbOynlyIcJ "Islandora 7 and Windows: Patches and Tips")).

When LAME is called through the command line in Windows, using single-quotes around the file names causes the command to fail. 

The following error message is generated:
> Could not find "'*&lt;NAME OF SOURCE FILE&gt;*'".

This is because Windows doesn't support single-quotes around file paths in the command line. Replacing them with double-quotes fixes the problem.