A few changes, the ultimate goal of which is to keep better track of the number of...

A few changes, the ultimate goal of which is to keep better track of the number of messages
that a mailbox currently has. A description of the changes:

1. Changed the "updated" field of the vm_state struct to act more as a binary semaphore than a
   counting semaphore, since its current implementation made the inboxcount function not work properly.
   This change falls in line with a change made by UPenn with their IMAP setup and helps to sync our changes with theirs.
2. Eliminated some redundant calls to get_vm_state_by_mailbox inside leave_voicemail
3. Use the play_folder variable to keep track of the number of old and new messages in a mailbox as the messages are deleted
4. Added an increment to the number of new messages that was not there previously in the leave_voicemail function

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.4@71877 65c4cc65-6c06-0410-ace0-fbb531ad65f3