Change /d2Zi+ flag on msvc builds to /Zo.

In Visual Studio 2013 Update 3, Microsoft removed the undocumented /d2Zi+ flag that wrote extra info to pdb files for optimized functions.

They added a new, documented flag with very similar but improved behavior, /Zo

http://msdn.microsoft.com/en-us/library/dn785163.aspx

(We already require VS2013 / msvc12 to build SM on Windows. The latest version of it at this time Update 4).