clears, and also to temporarily push the primary screen contents
into the scrollback while the alternate screen is active and bring
it back afterwards.
[originally from svn r2910]
to pieces, and put it back together in a new table-driven form.
config.c sets up a data structure describing most of the config box;
wincfg.c adds in the Windows-specific options (so that config.c can
also form the basis for Mac and Unix config boxes). Then winctrls.c
contains a shiny new layout engine which consumes that data
structure, and windlg.c passes all WM_COMMAND and similar messages
to a driver alongside that layout engine. In the process I've sorted
out nicer-looking panel titles and finally fixed the list-boxes-are-
never-the-right-size bug (turned out to be Windows's fault, of
course). I _believe_ it should do everything the old config box did,
including context help. Now everyone has to test it thoroughly...
[originally from svn r2908]
