t/shelltest.od: Add a new preliminary test for IFS= behaviour.

Apparently in zsh (when in sh compatibility mode), IFS=/ will split
"/a/b/c/" into 5 parts ("", "a", "b", "c", ""). Other shells all seem
to agree that it's 4 parts ("", "a", "b", "c"). zsh seems maybe more
correct to me, but the majority rules, so we'll warn on it.

Meanwhile, we'll also fix the one place in minimal/do that failed due
to this oddity, since it's relatively easy to avoid.

Reported-by: shamrin@gmail.com

t/shelltest.od

@@ -46,6 +46,15 @@ quiet_stderr()
 	fi
 }
 
+(
+	x="/a/b/c/"
+	IFS=/
+	f() {
+		[ "$2" = "a" ] || fail 2
+		[ "$#" = "4" ] || warn 2a
+	}
+	f $x
+)
 
 name=foo.o.o
 ext=.o