It seemed like it was intended as a mirror of cTown::difficulty, yet there didn't seem to
be anything that ever wrote to it.
So I just made everything use cTown::difficulty directly instead.
This commit only updates the XCode project for the changes.
A later commit each will update it for scons and MSVC.
A few actual changes are mixed in:
- Add a prefix header for a handful of common definitions
- Moved current_cursor into the Cursor class as a static member
- Removed the make_cursor_sword and make_cursor_watch functions
- Include tests in the All target
- Remove redundant -l flags for Common and Common-Party (since they're included in the Link phases anyway)