In preparation for adding a new Mac interface which will define a preprocessor macro...

In preparation for adding a new Mac interface which will define a preprocessor macro, MACH_O_COCOA, modified the header and source files where that preprocessor macro would be relevant.  The new Mac interface doesn't try to use things like creator codes (OS X still accepts them but no longer does anything with them) so there are places where the Mac interface doesn't follow what's set for MACH_O_CARBON.  Did not use MACH_O_CARBON for the new interface in case there's still interest for compiling Hengband for Macs running older versions of OS X.