t/*.do: add some time delays.

These only take effect if you export SLEEP=1.  Useful for testing
parallelism.

t/bellow.do

@@ -1,2 +1,3 @@
 redo-ifchange LD yellow.o
 ./LD bellow yellow.o
+./sleep 2

t/hello.do

@@ -1,2 +1,3 @@
 redo-ifchange LD hello.o
+./sleep 1
 ./LD hello hello.o

t/hello.o.do

@@ -1,3 +1,4 @@
 redo-ifchange CC hello.c /usr/include/stdio.h
 redo-ifcreate stdio.h
+./sleep 3
 ./CC hello.c

t/sleep

@@ -0,0 +1,4 @@
+PATH=/bin:/usr/bin
+if [ -n "$SLEEP" ]; then
+	exec sleep "$@"
+fi

t/yellow.do

@@ -1,2 +1,3 @@
 redo-ifchange LD yellow.o
+./sleep 1.5
 ./LD yellow yellow.o

t/yellow.o.do

@@ -1,2 +1,3 @@
 redo-ifchange CC hello.c
+./sleep 2
 gcc -o $3 -c hello.c