This function handles the interface for sending a new PM or replying to an existing one

• Accessed at index.php?action=pm;sa=send
• Checks permissions
• Loads the PersonalMessage template and language files (if you're not using wireless)
• Loads the InstantMessage template and/or language files if the appropriate PersonalMessage file doesn't exist (for compatibility)
• Uses the send sub-template
• If $_REQUEST['pmsg'] is specified, loads up that message and inserts it into the textarea in quote tags so you can quote it
• Loads up various other $context data for the template
• Finds memberNames for any user IDs specified by $_REQUEST['u'] if it's set
• Informs you of any errors that occurred when previewing or sending the PM