hg.py: add islocal() and defaultdest() functions, refactor islocal tells if a repo or url is local. defaultdest returns default path for clone if explicit path not given. clone can now take repo or url as source

#!/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