This addresses the bulk of <rdar://problem/15344950>, which involes us
not being able to find local variable declarations in expressions when
the parser didn't pre-bind them for us.
The fix to name lookup itself insures that a case such as
case (var a, a)
doesn't allow the second 'a' to find the first.
Swift SVN r9858
There is a special-case hack to allow capture of 'this', which is
implicitly [byref] for structs. At the moment, most of the cases where
this hack is necessary are [auto_closure] parameters (for assertions
and &&/||).
Swift SVN r5047
