While diagnosing the cause of a constraint system failure, being able to ignore some failures but not others allows us to produce slightly better error messages in some cases. This is in support of JoeG's current work.
Swift SVN r15560
a function conversion to be bad.
This encourages the type-checker to place conversions within
closures rather than outside; the test case here crashed in
SIL verification because of that. (Yes, that means that there's
an underlying problem still when the function conversion is
required; that's tracked by rdar://15875305.) But in general,
function conversions are likely to be expensive, and it's good
to avoid them when possible.
The setup work to add SK_FunctionConversion was accidentally
committed as part of r12813.
Swift SVN r12839
