All the data fields referring to the selection in 'struct gui_data'
have been pulled out into a separate structure of which there are now
multiple instances, and I've plumbed through what should be the right
pointers and integer ids to everywhere they should go. So now the GTK
front end defines CLIP_PRIMARY and CLIP_CLIPBOARD in place of the
temporary cop-out CLIP_SYSTEM from the previous commit, and copying
and pasting can be done via either one.
The defaults should be the same as before, except that now the non-Mac
versions of the GtkApplication front ends will access CLIP_PRIMARY in
response to most actions but the 'Paste' menu item will paste from
CLIP_CLIPBOARD. (That's mostly just as a demonstration that accessing
multiple clipboards even works.)
41aa675a5b