Changes from 25/5/2014.

Changelog:
2014.05.25:
- Changed the way in which we set the maximum output packet size for RTCP, because the previous
  hack (in "RTCP.cpp") wasn't 'thread safe'.  (Thanks to Liao ChunWei for noting this.)
- Moved "ourMD5.hh" from the "liveMedia" directory to the "liveMedia/include" directory,
  so as to make it accessible to applications.
  We also added a new function "our_MD5DataRaw()", which is similar to the existing
  "our_MD5Data()", except that it returns the digest as a 'raw' 16-byte buffer, rather than
  as an ASCII hex string.
- Added a "RemoveNext()" function to "AddressPortLookupServer".  (It just calls
  "HashTable::RemoveNext()".)