Use `-f` instead of `-e` in nvm_alias.
Use nvm_alias in nvm_ls.
Remove '-e' option from installation tests, in favor of explicit failures.
Two spaces after a period is incorrect.
Add note about Windows options. Related to #284.
Fixed links

The links were relative to github.com/creationix/nvm/master instead of the intended sites.
Merge pull request #544 from coreybutler/patch-1

Fixed links
Fix an output redirection error.
Ensure that we don't try to uninstall the current version of node in test teardowns.
Fixing "nvm alias" output redirection.
Fix `nvm alias` tests to have both stable and unstable mocks.
Don't list uninstalled implicit aliases
Properly handle nvm_print_implicit_alias splitting in zsh.

Hopefully fixes #546.
Fix npm update code

https://npmjs.org/install.sh redirects to https://www.npmjs.org/install.sh
so this code would fail if it ever npm was absent when we get here.
Merge pull request #548 from BanzaiMan/ha-bug-npm-update

Fix npm update code
Makefile enhanced to install required test utility 'urchin' on demand, locally, via `npm install`. The urchin install test was amended to also find a locally installed version, not just a global one as before.
Makefile enhanced to error out with instructions if invoked without a target.