I guess you're looking for:
MPC, music player command, is a command line tool to interface MPD, Music Player Daemon
..this is not part of the mpc (a library for the arithmetic of complex numbers with arbitrarily high precision and correct rounding of the result ) extension
Edit: OK, now I see the problem - in the 3.x repo, the music player was called mpc and it either wasn't copied over to the 4.x repo or it was overwritten by the complex number extension, mpc.
Since MPD is in capitals, maybe we could have an MPC extension for the music player?
Edit2: Had you submitted a more recent version than the one in the tc-3.x repo?