On second thought, use an empty string instead of "none" when not connected.

"none" could mislead to think that you're connected a database with that
name. Also, it needs to be translated, which might be hard without some
context. So in back-branches, use empty string, so that the message is
(currently ""), which is at least unambiguous and doens't require
translation. In master, it's no problem to add translatable strings, so use
a different fix there.

src/bin/psql/help.c

@@ -165,7 +165,7 @@ slashUsage(unsigned short int pager)
 
 	currdb = PQdb(pset.db);
 	if (currdb == NULL)
-		currdb = _("none");
+		currdb = "";
 
 	output = PageOutput(86, pager);