simplify make_filename, fix hg cat bug hg cat was using file-level rev/node ids for generating filename templates. This simplifies make_filename to only use changeset rev/node ids.

#!/bin/sh

hg init a
echo a > a/a
hg --cwd a ci -A -m a
hg clone a b
echo b > b/b
hg --cwd b ci -A -m b
chmod 100 a/.hg
hg --cwd b push ../a
chmod 700 a/.hg