swift234

fix <rdar://problem/22490787> QoI: Poor error message iterating over property with non-sequence type that defines a Generator type alias

which is a case where the only problem lurking in the constraint system is a disjunction
between two impossible to solve conversion constraints.  Arbitrarily pick the first one
so that we complain about *something*, instead of just calling the reference to path 
ambiguous.


Swift SVN r31886