Updated for System PHP and ZSH Compatibility

- ZSH/oh-my-zsh compatibility
- Can now use system PHP
- Clean up $PATH and $PHPRC
    * It was just pre-pending to $PATH, now removes all the PHP paths before
    adding the new one.
    * It will now clear $PHPRC before attempting to set. It could leave an
    old setting, if the new PHP version did not have a valid php.ini path.
Merge pull request #16 from jpscharf/mac-fixes-201309

Updated for System PHP and ZSH Compatibility