[CMake] Supported configurations with Visual Studio builds

[Josef Karthauser]

I’m confused (not for the first time! ☺). 

Why is it that cmGlobalVisualStudio7Generator only supports DEBUG, RELEASE, MINSIZEREL and RELWITHDEBINFO?  They’re mostly placeholders anyway so it seems wierd that they are hardcoded and enforced.

Is this a bug or a feature, does anyone know?  If I rip out the checks in cmGlobalVisualStudio7Generator:: GenerateConfigurations is anything going to break?

Joe