[PATCH] ni 660x pulse train generation

For those interested,

in attach a patch for the comedi ni660x driver that
- adds the possibility to disarm/arm a counter separately from its
   configuration stage.  This also allows
   * starting and stopping the counter using that arm instruction
   without having to rewrite the pulse_width and period.
   * altering period and pulse width using a write instruction if the
   counter is unarmed

   I've only added this for the pulse train generation, since I needed
   it over there :-)

- Chooses timebase3 (the maximum internal timebase of the board) as
   the default timebase for ptg.  This allows one to use the internal
   80 MHz clock for the 6602 board (instead of the 20 MHz clock used
   previously).  For the 6601, the maximum timebase is 20MHz, so
   nothing changes here.

This is not the refactoring of the driver I had in mind for a cold and
dark winter evening, but rather a quick hack, so I'm not sure this is
worth entering comedi.

ps.  Note that the include/linux/comedi.h part of the patch would also
have to be applied to comedilib.

regards,

Klaas