#267814 by liammcdermott, Berdir: Added feature with clean cut AHAH interface to control which author user roles are able to block receiving and/or sending of messages to recipient user role.

#376023 by Berdir + bugfix by litwol: #288183 followup: change hook_privatemsg_block_message to work on multiple recipients

#376250 by Berdir, nbz: Kill disallow_anon and introduce central message permissions API privatemsg_user_access

create branch 'DRUPAL-6--1'.

Cherrypick from master 2008-12-15 16:53:34 UTC Oleg Terenchuk <litwol@gmail.com> '#339565 by litwol: Fixed count query argument replacement':
    pm_block_user/pm_block_user.info
    pm_block_user/pm_block_user.install
    pm_block_user/pm_block_user.module
    privatemsg.test
    privatemsg_filter/privatemsg_filter.css
    privatemsg_filter/privatemsg_filter.info
    privatemsg_filter/privatemsg_filter.install
    privatemsg_filter/privatemsg_filter.module
    privatemsgapi/privatemsgapi.inc
    styles/privatemsg-list.css