BUG: return early with warning if no version of vc is found.
BUG: return early with warning if no version of vc is found.

timj/scons,timj/scons,andrewyoung1991/scons,timj/scons,timj/scons,andrewyoung1991/scons,timj/scons,andrewyoung1991/scons,andrewyoung1991/scons,timj/scons,andrewyoung1991/scons,timj/scons,andrewyoung1991/scons,timj/scons,andrewyoung1991/scons,andrewyoung1991/scons,timj/scons,andrewyoung1991/scons