[reSIProcate] DTLS committed

[nagendra modadugu <nagendra@xxxxxxxxxxxxxxx>]

(Owners of BaseSecurity.cxx and TuIM.cxx please read the whole message).

I just committed DTLS support to the tree.  Things to note:

* To compile with DTLS support, uncomment the 'USE_DTLS'
  switch in build/Makefile.conf

* DTLS source (basically mod'ed OpenSSL) lives under contrib/dtls.
  I'll push updates to this location as DTLS evolves.

* test/limpc can make DTLS connections when given the -dtlsPort flag

* test/limpc looks for certs under ~/.sipCerts/
  The server cert should be called domain_cert_test.pem and the
  corresponding private key domain_key_test.pem

* in the process of making DTLS work, I had to bypass two assert
  statements.  Could the respective owners of these files make sure
  that nothing is broken as a result.  The first assert is in
  BaseSecurity::addRootCertPEM, and the other in TuIM::haveCerts.

* I am in the process building a fresh tree to make sure that nothing
  is broken.  The build doesn't go through on Linux, but that was true
  even prior to my checkin.  I only access to OS X, so if any Windows
  user has trouble building, please let me know.