Remove special case for "dirname" -> "dirname/all"

It actually decreases readability of the .do files - by not making it
explicit when you're going into a subdir.

Plus it adds ambiguity: what if there's a dirname.do *and* a dirname/all?
We could resolve the ambiguity if we wanted, but that adds more code, while
taking out this special case makes *less* code and improves readability.
I think it's the right way to go.

t/deps/dirtest/t1.do

@@ -1,2 +1,2 @@
-redo-ifchange dir1/
+redo-ifchange dir1/all
 echo $$ >>log

t/deps/dirtest/t2.do

@@ -1,2 +0,0 @@
-redo-ifchange dir1
-echo $$ >>log

t/deps/dirtest/t3.do

@@ -1,2 +0,0 @@
-redo-ifchange dir1/all
-echo $$ >>log

t/deps/dirtest/test.do

@@ -1,19 +1,15 @@
-touch t?.do
-for first in t1 t2 t3; do
-	for second in t1 t2 t3; do
-		rm -f log dir1/log dir1/stinky
-		. ../../flush-cache.sh
-		redo $first
-		touch $second.do
-		. ../../flush-cache.sh
-		redo $second
-		. ../../flush-cache.sh
-		redo-ifchange $second
-		C1="$(wc -l <dir1/log)"
-		C2="$(wc -l <log)"
-		if [ "$C1" != 1 -o "$C2" != 2 ]; then
-			echo "failed: $first>$second, c1=$C1, c2=$C2" >&2
-			exit 55
-		fi
-	done
-done
+rm -f log dir1/log dir1/stinky
+touch t1.do
+. ../../flush-cache.sh
+redo t1
+touch t1.do
+. ../../flush-cache.sh
+redo t1
+. ../../flush-cache.sh
+redo-ifchange t1
+C1="$(wc -l <dir1/log)"
+C2="$(wc -l <log)"
+if [ "$C1" != 1 -o "$C2" != 2 ]; then
+	echo "failed: t1>t1, c1=$C1, c2=$C2" >&2
+	exit 55
+fi