Dominosa: another local deduction in Basic level.

Dominosa: another local deduction in Basic level.

This is necessary to solve the following test puzzle that someone sent
me in 2006 and I just recovered from my email archive:

6:65111036543150325534405211110064266620632365204324442053

Without this new deduction, the previous solver can't solve that
puzzle even at full power, but the half-solved state it leaves the
grid in has an obvious move in the top right corner (placing the 6-2
domino vertically in that corner forces two 3-0s to its left). Now
that kind of move can be made too, and the solver can handle this
puzzle (grading it as Hard).