pkgsrc: mplayer switches to the options framework

My little project these last two days has been to convert the mplayer packages to use the options framework and deprecate the old-style variables to tune its behavior. This is the "new" (has been around for a while already) way to go in pkgsrc, as it's cleaner, more homogeneous and more flexible.

During the conversion, I've added a lot more optional features in the package so that users can build a smaller package if wanted. Have fun ;)