Issue #1936866 by jonhattan: Drush dl needs to put files in /modules or /themes, not /sites/all/whatever.

#663290 by greg.1.anderson: Support 'required' options, and add a bunch of options to various command records that were missing that information.

unit tests can now derive from Drush_UnitTestcase and integration tests
will now use Drush_CommandTestCase

includes a bootstrap code reorganization in order to make this possible
and avoid code duplication

Feature #1173776 by moshe weitzman. A more complete --cache option for pm-download command. Optionally caches release XML and tarballs.

Setup Drupal files but don't install Drupal since thats slow and not needed for pm-download destination testing.

Add release XML testing. Again using php-eval via exec(). This time, using Nowdoc syntax to prepare a long string of PHP code for php-eval.

Add testVersionString which assures that pm-download is parsing release strings properly. An example of a unit test since it narrowly tests pm_parse_project_version(). It uses php-eval to do its bidding.

Added test for pm-download such that module goes to site specific dir cwd is in site specific dir ... Also added bootstrap=drush_testcase.inc to xml file so those who have customized need to copy that bit.