Merged revisions 312022 via svnmerge from

https://origsvn.digium.com/svn/asterisk/branches/1.8

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  r312022 | rmudgett | 2011-03-31 15:11:40 -0500 (Thu, 31 Mar 2011) | 14 lines
  
  chan_misdn segfaults when DEBUG_THREADS is enabled.
  
  The segfault happens because jb->mutexjb is uninitialized from the
  ast_malloc().  The internals of ast_mutex_init() were assuming a nonzero
  value meant mutex tracking initialization had already happened.  Recent
  changes to mutex tracking code to reduce excessive memory consumption
  exposed this uninitialized value.
  
  Converted misdn_jb_init() to use ast_calloc() instead of ast_malloc().
  Also eliminated redundant zero initialization code in the routine.
  
  (closes issue #18975)
  Reported by: irroot
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git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@312023 65c4cc65-6c06-0410-ace0-fbb531ad65f3