Memory leak fix

Memory leak fix

ast_xmldoc_printable returns an allocated block that must be freed by the
caller.  Fixed manager.c and res_agi.c to stop leaking these results.

(closes issue ASTERISK-22395)
Reported by: Corey Farrell
Patches:
     manager-leaks-11.patch uploaded by coreyfarrell (license 5909)
     res_agi-xmldoc-leaks.patch uploaded by coreyfarrell (license 5909)
........

Merged revisions 398060 from http://svn.asterisk.org/svn/asterisk/branches/1.8

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/11@398061 65c4cc65-6c06-0410-ace0-fbb531ad65f3