isearch transient msgs (e.g. case insensitive) - users to be able to adjust the sit-for time

[Drew Adams]

Any chance users could be able to adjust (via an option) the sit-for time
for the transient display of isearch messages like "case insensitive"?

In Emacs 20, such messages persisted slightly longer - long enough to see
them :-). How about either increasing the sit-for delay or letting users
adjust it themselves? Such messages go away when you type anyway, so why be
so stingy on the time to see them?