+ improve test/ncurses.c color-cycling test by reusing attribute-
and color-cycling logic from the video-attributes screen.
+ add ifdef'd with NCURSES_INTEROP_FUNCS experimental bindings in form
library which help make it compatible with interop applications
(patch by Juergen Pfeifer).
+ add configure option --enable-interop, for integrating changes
for generic/interop support to form-library by Juergen Pfeifer