minimal/do: don't create a .did file until after a file is actually built.

With the new "continue" feature on by default, it turned out that
ctrl-c during a build, or a .do file returning an error, would mark a
target as "built" even though it hadn't been.  This would prevent
retrying it when you started minimal/do again.  Use a temp file
instead.

It's a little tricky: to prevent accidental recursion, we want to
create a file *before* building, but clean up that file when starting
the next session.  And we rename that file to the actual .did file
*after* building successfully.

t/360-symlinks/.gitignore

@@ -1,4 +1,4 @@
-*.did
+*.ran
 *.extra
 a
 b

t/360-symlinks/a.do

@@ -1,4 +1,4 @@
-echo x >>a.did
+echo x >>a.ran
 rm -f $2.extra
 echo foo >$2.extra
 ln -s $2.extra $3

t/360-symlinks/all.do

@@ -1,14 +1,14 @@
-rm -f a a.extra b b.did
+rm -f a a.extra b b.ran
 d0=""
 redo a
 redo-ifchange b
-d1=$(cat b.did)
+d1=$(cat b.ran)
 [ "$d0" != "$d1" ] || exit 11
 
 # b only rebuilds if a changes
 ../flush-cache
 redo-ifchange b
-d2=$(cat b.did)
+d2=$(cat b.ran)
 [ "$d1" = "$d2" ] || exit 12
 
 . ../skip-if-minimal-do.sh
@@ -20,7 +20,7 @@ d2=$(cat b.did)
 ../flush-cache
 redo a
 redo-ifchange b
-d3=$(cat b.did)
+d3=$(cat b.ran)
 [ "$d2" != "$d3" ] || exit 13
 
 # Explicitly check that changing a's symlink target (a.extra) does *not*
@@ -30,5 +30,5 @@ d3=$(cat b.did)
 ../flush-cache
 touch a.extra
 redo-ifchange b
-d4=$(cat b.did)
+d4=$(cat b.ran)
 [ "$d3" = "$d4" ] || exit 14

t/360-symlinks/b.do

@@ -1,3 +1,3 @@
-echo x >>b.did
+echo x >>b.ran
 redo-ifchange a
 cat a >$3

t/360-symlinks/clean.do

@@ -1 +1 @@
-rm -f *~ .*~ a b *.extra *.did
+rm -f *~ .*~ a b *.extra *.ran