COMP: Fix the ExternalProject test for Visual Studio 6. Visual Studio 6 *.dsp files cannot have hyphens in them. Add utility function GetVS6TargetName to replace hyphens with underscores when generating *.dsp file names. Use the function everywhere necessary in the VS6 generators. And, a workaround: VS6 uses ".\Debug" (for example) as an "$(IntDir)" value - strip any leading ".\" when processing a --config argument in the cmake --build handling code.