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

minimal/do

@@ -196,7 +196,7 @@ _normpath()
 	fi
 	set -f
 	IFS=/
-	for d in $path; do
+	for d in ${path%/}; do
 		#echo "NP out='$out' d='$d'" >&2
 		if [ "$d" = ".." ]; then
 			out=$(_updir "${out%/}")/