Fix cursesw detection

On systems which do not provide ncursesw.pc and whose /usr/include/curses.h
does not include wide support, we should not only try with no -I, i.e.
/usr/include, but also with -I/usr/include/ncursesw.

To properly detect for wide support with and without -Werror, we need to
check for the presence of e.g. the WACS_DEGREE macro.

We also want to stop at the first curses_inc_list configuration which works,
and make sure to set IFS to : at each new loop.

Signed-off-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
Tested-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Message-id: 20161109102752.13255-1-samuel.thibault@ens-lyon.org
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
