Problem: popup: no opacity support for completepopup/previewpopup
Solution: Add support opacity: suboption for the 'completeopt'.
Accepts opacity:0-100 with the same semantics as popup_create()'s
opacity option, allowing the info / preview popup to blend with
the background.
closes: #20099
Signed-off-by: Yasuhiro Matsumoto <mattn.jp@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
59e59a62b4
