Adding some helpful output to `nvm copy-packages`
nvm install: Remove this redundant "already installed" check.
Extract --copy-packages-from argument.
Error out early if the --copy-packages-from version is invalid.
Copy packages when applicable, whenever `nvm install` would normally `nvm use` and exit.
Merge pull request #530 from creationix/copy_packages_from_on_install

nvm install: Add --copy-packages-from option
Removing an extra mkdir -p
Adding shell var quotes in `nvm alias`
Quote $NVM_DIR in commands
Compare shell variable contents with a sentinel.
Collapsing some if/else conditions with elif
Use $() instead of backticks; add quotes
More shellcheck recommendations
Use _ instead of ~ as a sentinel
Adding some more quotes and $()
v0.17.0
Suppress error messages in case there's no `master` branch.

Fixes #533.
Remove unnecessary local var declaration. Fixes #535
v0.17.1
Shell-quoting some more things.