Switch from /bin/sh to /bin/bash

You have bashisms in your script and /bin/sh might not always be bash. In that case the script would fail (for example on Ubuntu).
Remove unneeded shebang in nvm.sh
fix copy-packages in zsh

fixes #299, finally, using the local var syntax
fix MANPATH generation on FreeBSD

On FreeBSD, if MANPATH is set it is used verbatim; configuration
files are completely ignored.  Therefore, setting MANPATH to (only)
the nvm man dir makes system man pages unreachable.

To get around this, before doing anything else to MANPATH, if it is
empty set it to the output of manpath(1).

One further complication: FreeBSD automatically adds a path to the
man pages path for each path in PATH that ends in "/bin", which
causes "~/.nvm/$VERSION/man" to be added.  This interferes with the
subsequent substitution so strip this from MANPATH before the
substitution.
Merge pull request #278 from frasertweedale/fix/manpath

fix MANPATH generation on FreeBSD
readme: be inclusive of zsh when discussing shells

Much of the discussion in the README pertains to zsh as much as
bash, so include a specific reference to ~/.zshrc and remove one
explicit reference to bash.
Merge pull request #279 from frasertweedale/fix/readme-shell-names

readme: be inclusive of zsh when discussing shells
Merge branch 'master' into #299
Merge pull request #335 from naartjie/#299

fix copy-packages in zsh
export NODE_PATH on nvm use
Update NODE_PATH on use, run and deactivate
Update nvm.sh

Examples should point to latest stable release. ;)
Merge pull request #344 from dhoppe/patch-1

Update nvm.sh
Removed PREVIOUS_NODE_PATH
Merge pull request #342 from txgruppi/master

export NODE_PATH on nvm use
Fixes #346
Merge pull request #349 from zyxar/master

Fixes #346
Added mirror option for node binaries
Add dist to path, add docs
Merge pull request #245 from rgbkrk/mirror_z

Add mirror option for node binaries. Relates to #255.