Major addition to support DNS SRV resolution in PJSIP:
- added DNS asynchronous/caching resolver engine in
  PJLIB-UTIL (resolver.[hc])
- modified SIP resolver (sip_resolve.c) to properly
  perform DNS SRV/A resolution when DNS resolution is
  enabled.
- added dns_test.c in PJSIP-TEST for testing the SIP
  resolver.
- added nameserver configuration in PJSUA-LIB
- added "--nameserver" option in PJSUA.
- updated project/Makefiles and doxygen documentation.



git-svn-id: https://svn.pjsip.org/repos/pjproject/trunk@753 74dad513-b988-da41-8d7b-12977e46ad98
25 files changed