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/gitvars.do

@@ -0,0 +1,24 @@
+redo-ifchange gitvars.pre prodname
+
+read PROD <prodname
+
+# 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',
+# then the data will have been substituted already.  If we're in a checkout of
+# the git repo, then it won't, but we can just ask git to do the substitutions
+# right now.
+while read line; do
+	# Lines *may* be of the form: $Format: ... $
+	x=${line#\$Format:}  # remove prefix
+	if [ "$x" != "$line" ]; then
+		# git didn't substitute it
+		x=${x%\$}  # remove trailing $
+		if [ "$x" == "%d" ]; then
+			tag=$(git describe --match="$PROD-*")
+			x="(tag: $tag)"
+		else
+			x=$(git log -1 --pretty=format:"$x")
+		fi
+	fi
+	echo "$x"
+done <gitvars.pre