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>