Patch from Ben Hutchings to fix an error-checking goof: Keen

Patch from Ben Hutchings to fix an error-checking goof: Keen
division clues were failing to light up as erroneous if the quotient
of the numbers in them came out right under rounded-down C integer
division (e.g. 2 and 5 would be accepted for a 2/ clue). Apparently
I copied the code that invents clues in the generator straight into
the solution checker, without remembering that the generator was
allowed to do it that way because exact divisibility had been
checked elsewhere.

[originally from svn r8951]