Direct api to the native media player.

MediaPlayer.java has 3 new methods:
* newRequest creates a Parcel that can be used to send data to the
  native player using invoke.
* invoke issues synchronous calls to the native player using opaque
  parcels for the request and reply.

IMediaPlayer.h has 1 new abstract method:
* invoke

The Midi and Vorbis players have a stub for these. So far only PV
makes use of that new feature.

To avoid any copy overhead, the JNI interface uses Parcel as a java
object (no serialization/copy happens at the JNI layer).

The remote interface token is inserted when the Parcel is constructed
in java. That way the parcel is already routable when it reaches
 IMediaPlayer.cpp (proxy). No extra copy is needed there.