Generate redo version codes in Documentation/*.1 automatically.

We have to go through some pretty scary gyrations to extract this
information from git, but it can be done.  This works with both tarballs
generated by 'git archive', or with your local git repo.

(Requested by 'David' on the mailing list.)

version/vars.do

@@ -0,0 +1,40 @@
+redo-ifchange gitvars prodname
+
+read PROD <prodname
+
+exec <gitvars
+read COMMIT
+read NAMES
+read DATE
+
+# the list of names is of the form:
+#   (x,y,tag: $PROD-####,tag: $PROD-####,a,b)
+# The entries we want are the ones starting with "tag: $PROD-" since those
+# refer to the right actual git tags.
+names_to_tag()
+{
+	x=${1#\(}
+	x=${x%\)}
+	cur=
+	while [ "$cur" != "$x" ]; do
+		cur=${x%%,*}
+		cur=${cur#tag: }
+		cur=${cur## }
+		tagpost=${cur#$PROD-}
+		if [ "$cur" != "$tagpost" ]; then
+			echo "$tagpost"
+			return 0
+		fi
+		x=${x#*,}
+	done
+	commitpost=${COMMIT#???????}
+	commitpre=${COMMIT%$commitpost}
+	echo "unknown-$commitpre"
+}
+
+
+sTAG=$(names_to_tag "$NAMES")
+
+echo "COMMIT='$COMMIT'"
+echo "TAG='$sTAG'"
+echo "DATE='${DATE%% *}'"