swift234

Initial version of Swift.xcplugin, plus a convenient install script.

% utils/xcode/install.sh path/to/bin/swift

The "Name That Tune" Xcode project now contains a tiny little Swift CLI
program. It's fine to open the project without the xcplugin installed,
but if it is installed, you can select your modularized SDK and build/run
it in Xcode. (I'm hoping to make Foundation integration work out of the
box as well, but I can't test that because ObjC bridging is currently
broken.)

Tim, please add your xclangspec here!

Swift SVN r3442