swift234

The type checker is building RequalifyExpr's to strip off the @settable bit
in various unfortunate cases, which is really wrong and causing unpleasantness
for the new mutability model.  However, we can't fix this until the new 
mutability model lands.

To get from here to there, add some assertions to RequalifyExpr expr's ctor 
that are only enabled by the new model, to help me track down and purge these 
infractions.



Swift SVN r11445