Bridges solver enhancement. In the stage 3 solver, we were considering

Bridges solver enhancement. In the stage 3 solver, we were considering
the possibility that an island might form an isolated subgraph by
connecting to one of its neighbours (and, if so, reducing the maximum
bridge count in that direction so that some bridge would have to go
elsewhere), but we were not also considering the possibility that it
might form an isolated subgraph by connecting to _more_ than one of
its neighbours. For instance, if you have a 3 adjacent to a 1, a 2 and
something else, then at least one bridge must go to the something-else.

Previously insoluble test case:
10x10m2:a2b4a5a2a2a1ga2d3b33a3a4c2aa3e1a22b2a4b4aa3b1a2b33a1e3aa2a1a2c23a3a3a4a2a

[originally from svn r9543]