Update the version/format header info/comment to match MSVC 2013, apparently

to inform the MSVS version selector which IDE to open the solution file in.
This file was not updated during the migration from MSVC2010 to MSVC2013 and
appears to be another sighting of this bug:
https://connect.microsoft.com/VisualStudio/feedback/details/793984/sln-file-not-upgraded-to-vs2013-by-version-selector