By including only a single configuration type, visual studio
will bring that up by default.  This helps when building
release on windows, since you can restrict the projects to
only support release and avoid getting builds with both
libraries by mistake.  By passing this to the slicer project
you can open that and build without needing to remember to
change the build type.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@21499 3bd1e089-480b-0410-8dfb-8563597acbee