I'm actually quite surprised there was only _one_ copy of each of
these standard macros in the code base, given my general habit of
casually redefining them anywhere I need them! But each one was in a
silly place. Moved them up to the top level where they're available
globally.
This gets rid of all those annoying 'win', 'ux' and 'gtk' prefixes
which made filenames annoying to type and to tab-complete. Also, as
with my other recent renaming sprees, I've taken the opportunity to
expand and clarify some of the names so that they're not such cryptic
abbreviations.
