Problem: A function used through 'omnifunc' or 'complete' is called the
same way whether 'autocomplete' started the completion or a
key asked for one, so it cannot answer differently.
Solution: Report which of the two it is in complete_info() as "auto". It
is returned only when asked for in {what}, so what
complete_info() says by itself does not change
(Hirohito Higashi).
closes: vim/vim#211431f56c351de
Co-authored-by: Hirohito Higashi <h.east.727@gmail.com>