Add mkspec win32-msvc2013 and make VS 2013 known to configure and
qmake.
Change-Id: I6e63a4d679727a8a3f068f377956185996d72bce
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>