This has a number of small changes necessary for CoreFx support:

- Thread through the client directory to CommonCompiler.  This is
necessary for loading items like the SqmData.
- Move GetAssemblyVersion and GetAssemblyFileVersion into
CommonCompiler.  There is no need to specialize this for each compiler.
- Change the implementation of the above methods to not rely on
Assembly.Location which isn't present in CoreFx.

closes #1974