WIP: Write PDBs to stream instead of file

This enables writing the PDB to a memory-stream when shimming the
file-system. Code mostly converted from Roslyn
(http://source.roslyn.codeplex.com/#Microsoft.CodeAnalysis/InternalUtilities/ComStreamWrapper.cs,5dbd4388f94fa102)
That might work perfectly. Though, just from glossing over it, I can tell that it wouldn't work on on 64 bit windows systems.