Add autotools scripts to create VS2012 projects

Add autotools scripts to create VS2012 projects

As the project file format for Visual Studio 2012 is only slightly
different from Visual Studio 2010 projects, we can provide support for
building GLib (and other projects) with Visual Studio 2012 with relatively
little effort.  This might change when we eventually get GLib to work with
the Windows 8 (Modern UI/formerly Metro) APIs, but this will suffice for
the time being for people needing to build GLib with Visual Studio 2012.

Basically all that needs to be done at 'make dist' is:
-Copy the .sln/.props/README.txt/.vcxproj files and replace the VS2010
 stuff with VS2012 stuff
-Copy the .vcxproj.filters as is