redo-always/redo-ifcreate/redo-stamp: work inside chdir().

If someone cd's to another directory and then runs redo-always, we weren't
adding to the right target.

t/always1.do

@@ -1,3 +1,4 @@
 echo $$ >>always1.log
 echo $$
+cd ..
 redo-always

t/alwaystest.do

@@ -1,6 +1,8 @@
 rm -f always1 always1.log
 
-redo always1
+cd ..
+redo t/always1
+cd t
 [ "$(wc -l <always1.log)" -eq 1 ] || exit 11
 
 # This shouldn't rebuild, but because other people might be running flush-cache.sh
@@ -12,3 +14,12 @@ redo always1
 redo-ifchange always1
 . ./skip-if-minimal-do.sh
 [ "$(wc -l <always1.log)" -eq 2 ] || exit 31
+
+./flush-cache.sh
+redo-ifchange always1
+[ "$(wc -l <always1.log)" -eq 3 ] || exit 41
+
+cd ..
+./t/flush-cache.sh
+redo-ifchange t/always1
+[ "$(wc -l <t/always1.log)" -eq 4 ] || exit 51

t/stamp/stampy.do

@@ -1,4 +1,5 @@
 echo $$ >>stampy.log
 redo-ifchange inp bob
 cat inp
-redo-stamp <inp
+cd ..
+redo-stamp <stamp/inp