Merged revisions 339720 via svnmerge from

https://origsvn.digium.com/svn/asterisk/branches/10

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  r339720 | rmudgett | 2011-10-06 17:58:40 -0500 (Thu, 06 Oct 2011) | 27 lines
  
  Merged revisions 339719 via svnmerge from 
  https://origsvn.digium.com/svn/asterisk/branches/1.8
  
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    r339719 | rmudgett | 2011-10-06 17:47:50 -0500 (Thu, 06 Oct 2011) | 20 lines
    
    Fix regression in configure script for libpri capability checks.
    
    JIRA AST-598 added the PRI_L2_PERSISTENCE option to fix BRI PTMP TE layer
    2 persistence issues with some telcos.  ASTERISK-18535 attempted to fix
    the unexpected requirement that libpri *must* have that feature to work
    with Asterisk.  The AST_EXT_LIB_SETUP_DEPENDENT lines made the PRI
    optional features required.  Unfortunately, I thought
    AST_EXT_LIB_SETUP_DEPENDENT didn't do anything useful for libpri and
    deleted those lines for libpri.  The result was the HAVE_PRI_xxx defines
    that control the ability to use optional libpri features were also
    deleted.
    
    * Created AST_EXT_LIB_SETUP_OPTIONAL configuration macro to allow optional
    features in a library that the source code could take advantage of if the
    code supports the feature.
    
    (closes issue ASTERISK-18687)
    Reported by: Norbert
    Tested by: rmudgett
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git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@339721 65c4cc65-6c06-0410-ace0-fbb531ad65f3