Remove now unused --wrapper option from rez-config
Fix a bug with tempdir cleanup: use shutil.rmtree instead of os.removedirs, since the latter only removed empty directories.
Make PkgConflictErrors more legible.
Add a test package with 2 dimensional variants.  Add tools to packages for future testing of wrappers.
Make sure that VersionRange('') intersects properly with ExactVersionSets