swift234

Several changes:
 - Fix a diagnostic to not include redundant ''s around a type name.
 - Rework CleanupIllFormedExpression to be simpler and to not 
   unconditionally destroy data when it doesn't.  This makes a code 
   completion test a bit more precise.
 - Completely revamp getTypeOfIndependentSubExpression, to return the 
   subexpression produced by type checking instead of just a type.  This
   is important for cases when type checking changes the root of the AST
   (e.g. resolving an unresolved_dot_expr) and allows us to eliminate
   grungy and unsafe recovery code that was in place to work around this.

The last point makes the examples in Constraints/lvalues.swift better (giving
a somewhat generic error instead of an specific-but-incorrect error that 'z'
is immutable), but more importantly, it fixes a class of crashers like
<rdar://problem/21369926> Malformed Swift Enums crash playground service

where we'd end up with a LiteralExpr typed as Int instead of a Builtin integer
type of some sort.



Swift SVN r29932