drush_make 6.x-2.0-beta2

Mostly bug features but a few cool features including bzr support and tar file support.

Let's try out the not-so-awesome release note style:

Changes since DRUPAL-6--2-0-BETA1:

• #619072 by acrollet: Fixed patching functionality
• #619282 by dereine: Support bzr.
• #622224 by acrollet: Added support for .tar files.
• #622752 by lucidus_neil: Curl method of download always fails.
• #615570 by dmitrig01: Create a PATCHES.txt file.
• #623242 by e2thex: Fixed drush_make_updatexml() does not catch when release history xml was not found.
• Removed drush_make_shell_exec because it's now in drush core.