swift234

Solve different connected components in isolation, then combine the results.

Reduces type checking time for the standard library by ~13%, the
number of solver states visited by ~25%, and the number of pointlessly
visited constraints by ~30%. There are only 2175 separable
connected components in the standard library, likely because our
heuristics for picking type variables/constraints to solve bias
against connected components.



Swift SVN r10674