Merge pull request #203 from em-/master

Don't trust the environment and explicitly ask for the builtin `cd'
Fix the 'nvm deactivate' test

`nvm deactivate` does not really remove the nvm command, it just remove
the entries from $PATH and $MANPATH previously adde with `nvm use`.
Fix the setup/teardown urchin test scripts under zsh

The v* glob expansions were failing with an error under zsh, just set
nullglob/NULL_GLOB and make both bash and zsh happier.