[mythtv] New configure script automatically enabling XVMC

[Robert Kulagowski]

Pulled from CVS last night.  Running the configure script without any 
special options automatically added XVMC and XVMC-vld.  Net result was 
that going to Watch TV or Watch Recordings resulted in a black screen.

Re-ran ./configure  --disable-xvmc --disable-xvmc-vld 
--disable-joystick-menu

then recompiled, and all was good again. I think that the new configure 
script should stick with the old defaults, which I'm pretty sure didn't 
enable either of these.