Drush make moved into core Drush

The Drush Make project has been moved into core Drush. You should delete any existing drush_make commandfiles on your system. Existing makefiles should continue to work without modification.

While moving Make, we made the following changes:

1. New: Make concurrently downloads files thus massively speeding up processing.
2. New: Make caches already downloaded files thus even more massively speeding up subsequent runs.
3. New: Make's unit tests were expanded and ported to Drush's phpunit based system.
4. Change: See CVS integration project if you fetch from a CVS server.
5. Change: The ability to fetch files via POST method was removed. A contrib project could add it back if desired.