swift234

Expand the amount of unchecked_addr_casts that we can handle.

This is tested by an assertion in IRGen. After Beta3, this code is going
to go away and be replaced by just always promoting the cast. Then the
IRGen assertion will be replaced by propagating undef. The assertion in
the stdlib will still fire in that case since the assertion is based on
the tops not the given value implying that we will not lose any
correctness.

Swift SVN r19272