Change definitions of $1,$2,$3 to match djb's redo.

If you use "redo --old-args", it will switch back to the old
(apenwarr-style) arguments for now, to give you time to update your .do
scripts.  This option will go away eventually.

Note: minimal/do doesn't understand the --old-args option.  If you're using
minimal/do in your project, keep using the old one until you update your use
of $1/$2, and then update to the new one.

apenwarr-style default.o.do:
   $1      foo
   $2      .o
   $3      whatever.tmp

djb-style default.o.do:
   $1      foo.o
   $2      foo
   $3      whatever.tmp

apenwarr-style foo.o.do:
   $1      foo.o
   $2      ""
   $3      whatever.tmp

djb-style foo.o.do:
   $1      foo.o
   $2      foo.o  (I think?)
   $3      whatever.tmp

Documentation/md-to-man.do

@@ -1,8 +1,8 @@
 redo-ifchange md2man.py
 if ./md2man.py </dev/null >/dev/null; then
-	echo './md2man.py $1.md.tmp'
+	echo './md2man.py $2.md.tmp'
 else
 	echo "Warning: md2man.py missing modules; can't generate manpages." >&2
 	echo "Warning: try this: sudo easy_install markdown BeautifulSoup" >&2
-	echo 'echo Skipping: $1.1 >&2'
+	echo 'echo Skipping: $2.1 >&2'
 fi