[CMake] Supported configurations with Visual Studio builds

[Sylvain Benner]

> Is this a bug or a feature, does anyone know?  If I rip out the checks in cmGlobalVisualStudio7Generator:: GenerateConfigurations is anything going to break?
>
>   
If you rip out this I think you'll have an error with TRY_COMPILE. (be 
aware to delete your CMakeLists.txt cache each time you test your 
changes to be sure that the TRY_COMPILE is able to work correctly).

Well here I made a big hack like this in GenerateConfigurations method ^_^

    if (this->CMakeInstance->GetCacheDefinition("MP_CONFIGURATIONS_MODE"))
    {
        std::string sConfigurations = 
this->GetCMakeInstance()->GetCacheDefinition("CMAKE_CONFIGURATION_TYPES");
        this->Configurations.clear();
        cmsys::SystemTools::Split(sConfigurations.c_str(), 
this->Configurations, ';');
    }
    else
    {
        mf->AddCacheDefinition(
            "CMAKE_CONFIGURATION_TYPES",
            "Debug;Release;MinSizeRel;RelWithDebInfo",
            "Semicolon separated list of supported configuration types, "
            "only supports Debug, Release, MinSizeRel, and RelWithDebInfo, "
            "anything else will be ignored.",
            cmCacheManager::STRING);
        cmGlobalVisualStudio7Generator::GenerateConfigurations(mf);
    }

--Sylvain