swift234

Make all the subscripting getters/setters go down the same path.
This intentionally changes the mangling of variable getters and
setters so that we can have a reproducible mangling that doesn't
depend on things like the variables names, which is important
for resilience.  It's not currently important for subscripting,
although equally I see no reason to mangle in the subscript
pattern name.

Swift SVN r1590