swift234

Revert r30787, r30789, r30795, r30796, r30797

r30787 causes our tests to time out; the other commits depend on r30787.

Revert "revert part of my previous patch."
Revert "Produce more specific diagnostics relating to different kinds of invalid"
Revert "add a testcase, nfc"
Revert "- Reimplement FailureDiagnosis::diagnoseGeneralMemberFailure in terms of"
Revert "Fix places in the constraint solver where it would give up once a single "

Swift SVN r30805