[Bug-gnubg] Time control fixes

[Stein Kulseth]

- Fixed assertion failure from setting player on roll
- Fixed the bug of having the player's clock running
  while animating the computer move.
- Fixed a bug that stopped the GTK update of the running clock.
  I have still encountered this happening so there must be another
  bug with the same symptoms around somewhere, though ...
- Implemented swapping time info properly when swapping players.
- Made some GTK GUI for selecting time control and a (presently
  unfinished an non-functional) skeleton of GUI for defining
  time controls.
- Made a separate file with the example time controls, and updated
  the help text to say that you can open this with the open commands
  command. Maybe adding this to the autobgrc should be part of
  the installation, when we have release quality on the time controls
  feature. For now I think it is best that you have to open this yourself.

One thing not fixed:
  with tutor mode on, the human player is debited for the time GNUbg
  spends analyzing (human player's) cube decision and chequer play.

It is implemented this way by chance, rather than design, but I also think 
this is correct. The analysis helps the player - not the program. Anyhow, the 
combination of tutor mode and time control is slightly strange, so there may 
be no one right solution.

-- 
Stein Kulseth (address@hidden)