Fix symbol collision with pjsua.

We shouldn't be exporting any symbols that start with pjsip_.
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Merged revisions 398927 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: http://svn.asterisk.org/svn/asterisk/trunk@398928 f38db490-d61c-443f-a65b-d21fe96a405b