swift234

fix <rdar://problem/14096697> QoI: Diagnostics for trying to return values from void functions
by propagating the 'is return expr' bit more carefully in sequence folding, and by
adding another path for handling the return diagnostics better.

This probably improves a number of cases where we complain about "this argument list 
is invalid" when the call is in the context of a return.



Swift SVN r29565