Added support for VB pdb files 

VB pdb files can have temporary files created by the compiler.  These are included in the pdb with just the file names as the file path.  Not having an absolute path for a source file in the pdb breaks some assumptions made in other parts of the code.

A very simple fix.  The temporary files won't be added as a source file on the Symbol Server, but all the other VB source files will be.