The #definition of COMBINED was done very badly: it was a piece of
platform-dependent code in puzzles.h (ick), which in turn depended
on the magic symbol MAC_OS_X being defined by mkfiles.pl itself
(yuck). Suddenly realised I can do much better simply by putting it
in an OS X makefile extras section in Recipe, and removing both
previous hacks. Much nicer.

[originally from svn r5191]