Enhancements for glideFactoryLib.which
Comments from Doug's #2634 review:
2) which function in glideFactoryLib is useful. I think this should be pulled out into lib/subprocessSupport or exeSupport or something.
3) which function should also be documented more. The behavior for which('/tmp/python') for instance is to return None. That's the same as the which command, but could be clarified.
4) rrdtool_exe should use which
5) condorExe could use which