Ensure assemblies exist on disk before including them as referenced assemblies for dynamic compliation.

Currently all loaded assemblies are included as reference assemblies as supplied for dynamic compilation. If any of the actual files are missing it will fail, even if that assembly was not required.  This could occur if an assembly has been removed from the GAC without rebooting the server.
Merge pull request #78 from stefanmoser/release-3.0

Ensure assemblies exist on disk before including them as referenced assemblies for dynamic compliation