version/gitvars: use redo-always if using git commands.

Otherwise we won't rebuild files when the commit id changes.

version/gitvars.do

@@ -1,6 +1,7 @@
 redo-ifchange gitvars.pre prodname
 
 read PROD <prodname
+exec >$3
 
 # Fix each line from gitvars.pre where git may or may not have already
 # substituted the variables.  If someone generated a tarball with 'git archive',
@@ -12,6 +13,7 @@ while read line; do
 	x=${line#\$Format:}  # remove prefix
 	if [ "$x" != "$line" ]; then
 		# git didn't substitute it
+		redo-always   # git this from the git repo
 		x=${x%\$}  # remove trailing $
 		if [ "$x" = "%d" ]; then
 			tag=$(git describe --match="$PROD-*")
@@ -22,3 +24,5 @@ while read line; do
 	fi
 	echo "$x"
 done <gitvars.pre
+
+redo-stamp <$3