main/formats: Fix crash in ast_format_cmp during non-clean shutdown.

* Update asterisk.h to reflect availability of ast_register_cleanup in 11.9.
* Use ast_register_cleanup for format_attr_shutdown.

(closes issue ASTERISK-23103)
Reported by: JoshE
........

Merged revisions 411310 from http://svn.asterisk.org/svn/asterisk/branches/11


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/12@411311 f38db490-d61c-443f-a65b-d21fe96a405b