Changes from 3/10/2014.

Changelog:
2014.10.03:
- Fixed a problem in the "timestampString()" routine that occurs if "time_t" is 64 bits, but
  we're on a 32-bit machine.  (Thanks to Deanna Earley for reporting this.)
- Updated the debugging output code in "RTCP.cpp" to make it clearer that SDES and APP packets
  are not invalid; just not (yet) handled by us.