In BrewHelper#should_sudo, use #hypothetically_writable? to account for the case where /usr/local/Cellar doesn't exist, but `brew` would (and could) create it.
In BrewHelper#should_sudo, use #hypothetically_writable? to account for the case where /usr/local/Cellar doesn't exist, but `brew` would (and could) create it.

closes gh-159

victorklos/babushka,victorklos/babushka,victorklos/babushka