Clean up from some more tests
Show "∞" when there's a circular alias reference.
Prevent attempts to `nvm use` a circular reference.
use `command -p pwd` to use the system default pwd
use slash pwd instead of command
Merge pull request #560 from brock/pwd

use `command -p pwd` to use the system default pwd
Move sourcing tests to a separate test suite.
Testable install script

* wraps main code into a function
* EnvVar-based install start
* Clean environment after install