Add tests for "`nvm use default` on source" behavior.
Default $NVM_SYMLINK_CURRENT to off (create a "current" symlink on `use`).

Fixes #499.
README cleanup: Use the Oxford comma, properly lowercase commands
http://nodejs.org/dist now redirects to https://nodejs.org/dist
v0.17.3
Merge tag 'v0.17.3'
Ensure nvm follows redirects to nodejs.org
Ensuring that there's a stable and unstable version "available" for this test.
Prevent test pollution.
Adding nvm_resolve_alias
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.
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.
Changed `replace` npm package version spec. from ^ to ~.
`make list` now lists defined targets one line at a time.