swift234

Utilize argument type information to favor overload binding constraints on initializers. Doing so addresses a number of cases where the type checker was going exponential on seemingly simple user code.

Also, these changes fix the performance regressions that were introduced as a result of September's convertible/init requirement modifications, and allow us to roll back the associated workarounds that were added to the Adventure sample (rdar://problem/18942100).

Swift SVN r24520