Switched appengine_config to use site.addsitedir()

Replacing sys.path.insert() with site.addsitedir() makes it possible to import namespace package dependencies.
Fix 3rd party import order
Added comment
extracted the left-insertion logic into a separate module
Changed the import style.
made latest changes for consistency with Darth-Vendor.
Minor cleanup for consistency and added comments..
Typo.
Added module docstring.
vendor: switch to darth
vendor: add more comment about darth modifications
Merge pull request #1 from proppy/patch-1

vendor: switch to darth
vendor: restore artworks
Merge pull request #2 from proppy/patch-1

vendor: restore artworks
vendor: remove artwork docstring
Merge pull request #3 from proppy/patch-1

vendor: remove artwork docstring
Merge pull request #2 from webmaven/patch-1

Fixed 3rd-party package installation for namespace packages and overriding built-in libraries