t/660-stamp: don't run at the same time as other tests in redo -j.

flush-cache can cause files affected by redo-stamp to get rebuilt
unnecessarily, which the test is specifically trying to validate.
Since other tests run flush-cache at random times when using -j, this
would cause random test failures.

t/all.do

@@ -6,13 +6,26 @@ if [ "$(cat 000-set-minus-e/log)" != "ok" ]; then
     exit 5
 fi
 
-# builds 1xx*/all
+# builds 1xx*/all to test for basic/dangerous functionality.
+# We don't want to run more advanced tests if the basics don't work.
 /bin/ls 1[0-9][0-9]*/all.do |
 sed 's/\.do$//' |
 xargs redo
 110-compile/hello >&2
 
-# builds the rest
+# builds most of the rest in parallel
 /bin/ls [2-9][0-9][0-9]*/all.do |
 sed 's/\.do$//' |
 xargs redo
+
+# builds the tests that require non-parallel execution.
+# If tests are written carefully, this should only be things that
+# are checking for unnecessary extra rebuilds of some targets, which
+# might happen after flush-cache.
+# FIXME: a better solution might be to make flush-cache less destructive!
+/bin/ls [s][0-9][0-9]*/all.do |
+sed 's/\.do$//' | {
+    while read d; do
+        redo "$d"
+    done
+}

t/s60-stamp/stamptest.do

@@ -1,4 +1,4 @@
-rm -f stampy usestamp usestamp2 stampy.log usestamp.log usestamp2.log
+rm -f bob stampy usestamp usestamp2 stampy.log usestamp.log usestamp2.log
 echo one >inp
 
 ../flush-cache

t/s60-stamp/stampy.do

@@ -2,4 +2,4 @@ echo $$ >>stampy.log
 redo-ifchange inp bob
 cat inp
 cd ..
-redo-stamp <660-stamp/inp
+redo-stamp <s60-stamp/inp