Use symbolic names for standard file descriptors.

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>
src/editor/editbuffer.c: typo.

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>
doc/NEWS: cosmetics.

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>