redo-log: add automated tests, and fix some path bugs revealed by them.

When a log for X was saying it wanted to refer to Y, we used a relative
path, but it was sometimes relative to the wrong starting location, so
redo-log couldn't find it later.

Two examples:

 - if default.o.do is handling builds for a/b/x.o, and default.o.do
   does 'redo a/b/x.h', the log for x.o should refer to ./x.h, not
   a/b/x.h.

 - if foo.do is handling builds for foo, and it does
   "cd a/b && redo x", the log for foo should refer to a/b/x, not just
   x.

t/370-logs/.gitignore

@@ -0,0 +1,3 @@
+pid
+x
+y

t/370-logs/a/b/xlog.do

@@ -0,0 +1,5 @@
+read pid <../../pid
+
+# Test that log retrieval works correctly when run from a different base dir.
+redo-log -ru ../../x | grep -q "^$pid x stderr" || exit 45
+redo-log -ru ../../x | grep -q "^$pid y stderr" || exit 46

t/370-logs/all.do

@@ -0,0 +1,52 @@
+exec >&2
+rm -f x pid
+pid=$$
+echo "$pid" >pid
+xout=$(redo x)
+
+[ "$(printf "$xout" | wc -l)" -eq 0 ] || exit 2
+
+if [ -n "$REDO_LOG" ]; then
+	# redo has redo-log support enabled, so check that it saves logs.
+
+	# recursive log dump should show both x and y stderr.
+	redo-log -ru x | grep -q "^$pid x stderr" || exit 10
+	redo-log -ru x | grep -q "^$pid y stderr" || exit 11
+
+	# stdout captured by redo into the files x and y, *not* to log
+	redo-log -ru x | grep -q "^$pid x stdout" && exit 20
+	redo-log -ru x | grep -q "^$pid y stdout" && exit 21
+	[ "$(cat x)" = "$pid x stdout" ] || exit 22
+	[ "$(cat y)" = "$pid y stdout" ] || exit 23
+
+	# non-recursive log dump of x should *not* include y
+	redo-log x | grep -q "^$pid y stdout" && exit 30
+	redo-log x | grep -q "^$pid y stderr" && exit 31
+
+	redo a/b/xlog
+	(cd a && redo b/xlog)
+
+        # Test retrieval from a different $PWD.
+        (
+            cd a/b || exit 40
+            redo-log -ru ../../x | grep -q "^$pid x stderr" || exit 41
+            redo-log -ru ../../x | grep -q "^$pid y stderr" || exit 42
+        ) || exit
+fi
+
+# whether or not redo-log is available, redirecting stderr should work.
+pid=$$-bork
+rm -f x pid
+echo "$pid" >pid
+out=$(redo x 2>&1)
+
+# x's stderr should obviously go where we sent it
+echo "$out" | grep -q "^$pid x stderr" || exit 50
+
+# This one is actually tricky: with redo-log, x's call to 'redo y' would
+# normally implicitly redirect y's stderr to a new log.  redo needs to
+# detect that we've already redirected it where we want, and not take it
+# away.
+echo "$out" | grep -q "^$pid y stderr" || exit 51
+
+exit 0

t/370-logs/clean.do

@@ -0,0 +1 @@
+rm -f *~ .*~ all x y pid

t/370-logs/x.do

@@ -0,0 +1,5 @@
+read pid <pid
+echo "$pid x stdout"
+echo "$pid x stderr" >&2
+rm -f y
+redo y

t/370-logs/y.do

@@ -0,0 +1,3 @@
+read pid <pid
+echo "$pid y stdout"
+echo "$pid y stderr" >&2