... because the two macros have the same expansion, and are both checked for
in the --keyword arguments passed to msgfmt by locale/update_po_files.sh.
This commit makes ONLY such changes, and comments in Internat.h. It is big
but quite harmless.
The intention is to introduce a type distinction in a later release, by defining
XXO differently. XXO is used where & characters in strings (for hotkeys of menu
items or control prompts) are permitted, XO where not.