Added correct path for mspdb120.dll for VS2013.

The mspdb120.dll file for all architectures is now stored in %VCINSTALLDIR%\bin in VS2013. I've added that path to the VC2013 path.
Merge pull request #3499 from LightBender/patch-1

Added correct path for mspdb120.dll for VS2013.
Move test case for issue 12211 to runnable/assignable.d
fix Issue 12650 - Invalid codegen on taking lvalue of instance field initializing
Merge pull request #3500 from 9rnsr/fix12650

[REG2.066a] Issue 12650 - Invalid codegen on taking lvalue of instance field initializing