Make sure `nvm ls foo` returns a nonzero exit code when a version is not found.

Fixes #440.
Make sure these vars are local, where supported
Don't bother trying to return the exit code of `nvm alias` or `nvm_print_versions`
Merge pull request #444 from creationix/fix_nvm_ls

Make sure `nvm ls foo` returns a nonzero exit code when a version is not found
v0.10.0
Use bash, not sh for install scritps

Install scripts don't work in pure sh; they may work on some systems where
the /bin/sh binary actually implements more than the pure Bourne Shell but
fail on other ones (e.g. Ubuntu).

Just using bash works.
Merge pull request #450 from mzgol/install-script

Use bash, not sh for install scritps
Oxford comma
Use "typeset" instead of "local" for portability