Prevent spurious memory error when appending backtrace with MALLOC_DEBUG

Backtraces are allocated outside of the usual memory tracking performed by
MALLOC_DEBUG. This allows them to be used by the memory tracking enabled
by that build option; however, it also means that when backtraces are
disposed of they have to be done so outside of the re-defined free.

This patch undef's free prior to disposing of the allocated backtrace when
a backtrace is appended as a result of 'core show locks'.


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@396391 65c4cc65-6c06-0410-ace0-fbb531ad65f3