swift234

thoroughly rework how the REPL synthesizes code to print values.  This centralizes the
logic in Sema (previously, some of it was in tools/Swift/Frontend.cpp) and eliminates
redundancy between expr and pattern printing.  This also eliminates most of the invalid
ASTs that the repl was producing (there is still one left).

This commit reenables the disabled REPL testcase from my last big change.



Swift SVN r4622