Change some uses of free() to ast_free(). (No functional differences.)

(closes issue #11138)
Reported by: eliel
Patches: 
      pbx_dundi.c.patch uploaded by eliel (license 64)
	  chan_sip.c.patch uploaded by eliel (license 64)


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@88077 65c4cc65-6c06-0410-ace0-fbb531ad65f3