Fix findings from check-in on r374177

Fix findings from check-in on r374177

Richard pointed out two problems with the check-in from r374177:
* The ast_msg_shutdown function declaration doesn't match the prototype
  in main/message.c.
* The ref/alloc function usage in astobj2 (in trunk) can use the ao2_t_*
  variants of the functions to allow the REF_DEBUG flag to enable/disable
  their debug counterparts.
........

Merged revisions 374210 from http://svn.asterisk.org/svn/asterisk/branches/10

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/11@374211 65c4cc65-6c06-0410-ace0-fbb531ad65f3