Fix a bug causing premature defeatism in the Bridges solver. Deducing

Fix a bug causing premature defeatism in the Bridges solver. Deducing
a better upper bound on the number of bridges leaving a given island
in a given direction was not counted as having 'done something'; so a
solver run could make several such deductions, but then terminate in
the belief that it hadn't achieved anything, when just going back
round the main solver loop would have enabled it to make further
deductions based on those new bounds.

[originally from svn r9377]