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

echo "Is there an error message when trying to diff non-existing files?"
hg diff not found

echo "Is there an error message when trying to add non-existing files?"
hg add not found