Add "$COMMONPROGRAMFILES\Merge Modules" (on current versions of Windows
that probably is "C:\Program Files (x86)\Common Files\Merge Modules") as
fallback, since for example on Windows Server 2012, the registry entry
has not been created when installing Visual Studio Express

Change-Id: I16f58b8a1d453c8628c6eb66c2cea37ab3da913a
Reviewed-on: https://gerrit.libreoffice.org/3680Reviewed-by: Tor Lillqvist <tml@iki.fi>
Tested-by: Tor Lillqvist <tml@iki.fi>