Merged revisions 221769 via svnmerge from

https://origsvn.digium.com/svn/asterisk/branches/1.4

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  r221769 | rmudgett | 2009-10-01 18:18:28 -0500 (Thu, 01 Oct 2009) | 26 lines
  
  Occasionally losing use of B channels in chan_misdn.
  
  I have not been able to reproduce the problem of losing channels.
  However, I have seen in the code a reentrancy problem that might give
  these symptoms.
  
  The reentrancy patch does several things:
  1) Guards B channel and B channel structure allocation.
  2) Makes the B channel structure find routines more precise in locating records.
  3) Never leave a B channel allocated if we received cause 44.
  
  The last item may cause temporary outgoing call problems, but they should
  clear when the line becomes idle.
  
  (closes issue #15490)
  Reported by: slutec18
  Patches:
        issue15490_channel_alloc_reentrancy.patch uploaded by rmudgett (license 664)
  Tested by: rmudgett, slutec18
  
  (closes issue #15458)
  Reported by: FabienToune
  Patches:
        issue15458_channel_alloc_reentrancy.patch uploaded by rmudgett (license 664)
  Tested by: FabienToune, rmudgett, slutec18
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