Fix for issue #95.

- Adds an 'ignore' option to `release_info_fetch` that is used by drush
  make when only project type is needed from release info.

Signed-off-by: Jonathan Hedstrom <jhedstrom@gmail.com>
Issue #95: Use drush_set_error instead of user_abort.

Signed-off-by: Jonathan Hedstrom <jhedstrom@gmail.com>