core: Introduce chaos into memory allocations

Locate potential crashes by exercising seldom
used code paths.  This patch introduces a new
define DEBUG_CHAOS, and mechanism to randomly
return an error condition from functions that
will seldom do so.  Functions that handle the
allocation of memory get the first treatment.

Review: https://reviewboard.asterisk.org/r/4463/
........

Merged revisions 433060 from http://svn.asterisk.org/svn/asterisk/branches/13


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@433063 65c4cc65-6c06-0410-ace0-fbb531ad65f3