ENH: Make it easier to use configure/make/make-install as the build steps for an external project. Add capability of customizing the download step. Add tests of empty projects. Better comments and error checking in AddExternalProject.cmake. In tests, use KWStyle from CVSHEAD to see if QNX continuous can build the latest KWStyle. Make KWStyle test depend on all previous test external projects so it builds last to catch other issues before any KWStyle compile errors.