Adds a FLAG_SKIP_FEC field to Buffer. In RTPSourceStream, sets this flag to Buffers read from the queue right after a Buffer was discarded from the queue.

git-svn-id: http://svn.code.sf.net/p/fmj/code/fmj@25 799b4810-d841-4bb4-a54b-9156a0c3e4cd