swift234

Initial set of changes to add a new 'swift_driver' executable.

- Added a couple of new targets:
  - libswiftDriver, which contains most of the driver implementation
  - swift_driver, which produces the actual executable

- Added centralized version information into libswiftBasic.

- Added a new "Driver Design & Internals" document, which currently describes
  the high-level design of the Swift driver.

- Implemented an early version of the functionality of the driver, including
  versions of the Parse, Pipeline, Bind, Translate, and Execute driver stages.
  Parse, Pipeline, and Bind are largely implemented; Translate and Execute are
  early placeholders. (Translate produces "swift_driver --version" and "ld -v"
  commands, while Execute performs all subtasks sequentially, rather than in
  parallel.)

This is just the starting point for the Swift driver. Tests for the existing
behavior are forthcoming.

Swift SVN r10933