CheckSourceInInstall correctly installs current vtk-m files
requested to merge robertmaynard/vtk-m:CheckSourceInInstall_now_handles_dirty_build_dirs into master
Previously we didn't realize that the cmake_install.cmake files would properly walk the entire install tree. Therefore we would try to find each one manually and invoke it. This caused problems with dirty continuous build directories, and was actually unneeded as just including the root cmake_install.cmake is sufficient.