When gathering constraints for a type variable, we were gathering all of
the constraints for the members of the equivalence class, and then for
the adjacencies of the representative of the equivalence class, but not
from the adjacencies of other members of the equivalence class.
For example for:
#3 = $T3
#4 = $T4 equivalent to $T3
#5 = $T5 as $T4.Element
after binding $T3 we would collect the constraints related to $T3 and
$T4, but not $T5. The end result can be that we finish examining all
disjunctions and type bindings but still have inactive constraints in
the constraint graph, which is treated as a failure in the solver.
Fixes SR-5120 / rdar://problem/32618740.
