Improved OS X support
- Improved some of the language in the README.
- Added support for compiling under OpenCL 1.0.
- Fixed numerous issues with the Xcode project output paths.
- Added an Xcode project for opencl_test.
- Added support for compiling both CLcpp and opencl_test under OS X using SCons.
- Changed the target toolsets in the SConstruct files for Linux and OS X; both platforms use GCC by default, so it made more sense to have them set as 'default'.
- Corrected a few problems in opencl_test that were exposed by compiling and running on OS X (in an attempt to make opencl_test as universal as possible).