Improve zsh setup script for Linux

The script wasn't pointing to the right zshrc file, now it does

The script didn't install oh-my-zsh until now.
Fix zsh setup script for Linux

The script was checking for curl twice instead of checking for Git that
second time.

I also add the -y option to the apt-get install commands so that there
would be no dialog for installing zsh, curl, and Git.
Improve zsh setup script for OSX

The installer now installs oh-my-zsh, along with checking for curl and
git when before it tries to install oh-my-zsh.

All these changes are coming out nicely!