avoid duplicates and extra noise when there are other messages.

Added as a user option, so any user can turn this off.
Also omit (0) after "my inbox" in menu link if there are no new messages.

privatemsg, to avoid error if not logged in (if already logged in, drupal
will redirect right to privatemsg)

create branch 'DRUPAL-4-7'.

Sprout from master 2006-06-09 14:53:06 UTC Alan Harder <mindless@33033.no-reply.drupal.org> 'Rollup of 8 pending patches, see http://drupal.org/node/67612'
Cherrypick from master 2006-06-09 18:33:03 UTC Alan Harder <mindless@33033.no-reply.drupal.org> 'Add table creation and utf8 update into privatemsg.install file':
    privatemsg.install

http://drupal.org/node/37691