Half-support for using file checksums instead of stamps.

A new redo-stamp program takes whatever you give it as stdin and uses it to
calculate a checksum for the current target.  If that checksum is the same
as last time, then we consider the target to be unchanged, and we set
checked_runid and stamp, but leave changed_runid alone.  That will make
future callers of redo-ifchange see this target as unmodified.

However, this is only "half" support because by the time we run the .do
script that calls redo-stamp, it's too late; the caller is a dependant of
the stamped program, which is already being rebuilt, even if redo-stamp
turns out to say that this target is unchanged.

The other half is coming up.

t/clean.do

@@ -1,5 +1,5 @@
-redo example/clean curse/clean deps/clean "space dir/clean"
-rm -f c c.c c.c.c c.c.c.b c.c.c.b.b d mode1 makedir.log chdir1 \
+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
 rm -rf makedir

t/stamp/.gitignore

@@ -0,0 +1,4 @@
+/*.log
+/usestamp
+/stampy
+/inp

t/stamp/clean.do

@@ -0,0 +1 @@
+rm -f *.log usestamp stampy inp *~ .*~

t/stamp/stamptest.do

@@ -0,0 +1,29 @@
+rm -f stampy usestamp stampy.log usestamp.log
+echo one >inp
+
+../flush-cache.sh
+redo stampy
+[ "$(wc -l <stampy.log)" -eq 1 ] || exit 11
+
+redo-ifchange usestamp
+[ "$(wc -l <stampy.log)" -eq 1 ] || exit 21
+[ "$(wc -l <usestamp.log)" -eq 1 ] || exit 12
+
+../flush-cache.sh
+redo stampy
+[ "$(wc -l <stampy.log)" -eq 2 ] || exit 31
+[ "$(wc -l <usestamp.log)" -eq 1 ] || exit 32
+
+redo-ifchange usestamp
+[ "$(wc -l <stampy.log)" -eq 2 ] || exit 41
+[ "$(wc -l <usestamp.log)" -eq 1 ] || exit 42
+
+../flush-cache.sh
+echo two >inp
+redo stampy
+[ "$(wc -l <stampy.log)" -eq 3 ] || exit 51
+[ "$(wc -l <usestamp.log)" -eq 1 ] || exit 52
+
+redo-ifchange usestamp
+[ "$(wc -l <stampy.log)" -eq 3 ] || exit 61
+[ "$(wc -l <usestamp.log)" -eq 2 ] || exit 62

t/stamp/stampy.do

@@ -0,0 +1,3 @@
+echo $$ >>stampy.log
+cat inp
+redo-stamp <inp

t/stamp/test.do

@@ -0,0 +1 @@
+redo stamptest

t/stamp/usestamp.do

@@ -0,0 +1,3 @@
+redo-ifchange stampy
+echo $$ >>usestamp.log
+cat stampy

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
+	silencetest touchtest stamp/test