Switch the way we configure for MediaPlayer retransmission.

Move in the direction of a more publishable API for configuring a
media player for retransmission.  It used to be that we used a custom
invoke and a modified URL (prefixed with aahTX://).  There are many
issues with this technique and it was never meant to stand the test of
time.

This CL gets rid of all that.  A new (but currently hidden) method was
introduced to the java level MediaPlayer API, called
setRetransmitTarget(InetSocketAddress), which allows an app writer to
set the retransmit target.  For now, this method needs to be called
before a call to setDataSource (which is pretty unusual for the
MediaPlayer API) because this mid level code uses this as a cue to
instantiate an aahTX player instead of relying on the data source to
select a player.  When retranmit functionality becomes part of the
existing android player implemenation, this
set-retrans-before-set-data-source behavior can go away, along with
the aahTX player itself.

Change-Id: I6ab07d89b2eeb0650e634b8c3b7a0b36aba4e7dd