redo.py: shuffle the list of targets.
redo.py: shuffle the list of targets.

This encourages greater randomness in builds, which both decreases lock
contention and should help with testing the consistency of parallel builds.

pombredanne/redo,apenwarr/redo,dinkelk/redo-python,pombredanne/redo,pombredanne/redo,dinkelk/redo-python,apenwarr/redo,pombredanne/redo,apenwarr/redo,apenwarr/redo,rowhit/redo,rowhit/redo,rowhit/redo,dinkelk/redo-python,rowhit/redo,dinkelk/redo-python