Bug 784841 - Part 6: Move some functions from ConfigStatus to mozbuild; r=ted

--HG--
rename : build/tests/unit-ConfigStatus.py => python/mozbuild/mozbuild/test/backend/test_configenvironment.py
Bug 784841 - Part 7: Implement recursive make backend; r=ted
Bug 784841 - Part 8: Capture and save moz.build tree state; r=ted
Bug 784841 - Part 9: Ability to define external projects in moz.build files; r=ted
Bug 784841 - Part 10: Add warning() and error() functions to moz.build files; r=ted
Bug 784841 - Part 11: Add CONFIGURE_SUBST_FILES to moz.build files; r=ted