configure: warn against --enable-client=gtk3 when gtk3.22 available
From https://www.hostedredmine.com/issues/853912 :
"maybe our configure should informa a user who has gtk+-3.22 / 3.24, but does --enable-client=gtk3 anyway that gtk3.22-client might be better suited for them."
Patch meant for S3_0 & S3_1 - there's no issue to resolve in master as it doesn't have gtk3-client at all.
From https://www.hostedredmine.com/issues/853912 :
"maybe our configure should informa a user who has gtk+-3.22 / 3.24, but does --enable-client=gtk3 anyway that gtk3.22-client might be better suited for them."