"set keywords" grayed out for folders (no recursion allowed) (bug 467303)

https://bugs.eclipse.org/bugs/show_bug.cgi?id=467303

git-svn-id: https://dev.eclipse.org/svnroot/technology/org.eclipse.subversive/trunk@21475 ee007c2a-0a25-0410-9ab9-bf268980928c