Fixes numerous issues in PSM

Some Details

78fcd7 - Allowing MP3 files to load under PSM

35ac85e, 24fbbe7 - Reverting a recent change that broke font and vector functions under PSM that were previously working in cross platform code in XNA, PSM, Xbox360, iOS, OSX and Android.

4f8fb2b - There was a missing assignment to GraphicsDevice in private Texture2D(GraphicsDevice graphicsDevice, Stream stream) for PSM that was causing a null reference exception reported here. http://monogame.codeplex.com/discussions/492456

4e624e6, b3e3f22 - Please check this carefully...  I think is this be because I started working on a branch of develop that was very old.