Add a redo-always command: it adds an "always dirty" dependency to your target.

This is mostly useless except when combined with redo-stamp... I think.

t/.gitignore

@@ -16,3 +16,5 @@ test2.args
 /touch1
 /touch1.do
 /deltest2
+/always1
+/always1.log

t/always1.do

@@ -0,0 +1,3 @@
+echo $$ >>always1.log
+echo $$
+redo-always

t/alwaystest.do

@@ -0,0 +1,13 @@
+rm -f always1 always1.log
+
+redo always1
+[ "$(wc -l <always1.log)" -eq 1 ] || exit 11
+
+# This shouldn't rebuild, but because other people might be running flush-cache.sh
+# in parallel with us, we can't be 100% sure it won't.  So don't test it.
+#redo-ifchange always1
+#[ "$(wc -l <always1.log)" -eq 1 ] || exit 21
+
+./flush-cache.sh
+redo-ifchange always1
+[ "$(wc -l <always1.log)" -eq 2 ] || exit 31

t/clean.do

@@ -1,5 +1,5 @@
 redo example/clean curse/clean deps/clean "space dir/clean" stamp/clean
 rm -f c c.c c.c.c c.c.c.b c.c.c.b.b d mode1 makedir.log chdir1 deltest2 \
-	hello [by]ellow *.o *~ .*~ CC LD passfail silence silence.do \
-	touch1 touch1.do
+	hello [by]ellow *.o *~ .*~ *.log CC LD passfail silence silence.do \
+	touch1 touch1.do always1
 rm -rf makedir

t/stamp/stamptest.do

@@ -7,6 +7,7 @@ redo stampy
 
 # stampy already exists, so we won't generate it a second time, even though
 # usestamp depends on it.
+../flush-cache.sh
 redo-ifchange usestamp
 [ "$(wc -l <stampy.log)" -eq 1 ] || exit 21
 [ "$(wc -l <usestamp.log)" -eq 1 ] || exit 12
@@ -17,6 +18,7 @@ redo stampy
 [ "$(wc -l <usestamp.log)" -eq 1 ] || exit 32
 
 # same as above: stampy is already up-to-date, so it won't be redone.
+../flush-cache.sh
 redo-ifchange usestamp
 [ "$(wc -l <stampy.log)" -eq 2 ] || exit 41
 [ "$(wc -l <usestamp.log)" -eq 1 ] || exit 42

t/test.do

@@ -2,4 +2,4 @@ redo-ifchange all
 ./hello >&2
 redo deltest deltest2 test.args test2.args passfailtest chdirtest \
 	curse/test deps/test "space dir/test" modetest makedir2 \
-	silencetest touchtest stamp/test
+	silencetest touchtest stamp/test alwaystest