swift234

[PrintAsObjC] Use the selectors provided by the AST.

...instead of building our own from the argument patterns. This is all likely
to change soon, so let's not keep a separate implementation in PrintAsObjC.

In that vein, print subscript accessors the same way as any other methods.

No functionality change, except that subscript setter arguments are not all
called "value" any more.

Swift SVN r15532