fix PATCHLEVEL

fix PATCHLEVEL

> Somebody has changed versioning so that the game incorrectly states
> 3.6.1 in messages. It looks like someone updated patchlevel instead of
> editlevel?

Yes, that was me.  I meant to increment EDITLEVEL and nobody noticed
the mistake until now....

This changes PATCHLEVEL back to the correct value of 0, and implicitly
resets EDITLEVEL to 0 for release (by not changing it to 1 as it was
supposed to have been for the past 3-4 weeks).

Data files from Oct. 18 through today are actually compatible but will
be rejected once anyone rebuilds with this fix, same as would happen
when EDITLEVEL changs.  Data files from before Oct. 18 will be
incompatible but be accepted by nethack but not work correctly due to
a change in the 'context' structure.