Adds better headers.

Signed-off-by: Markus Hubig <mhubig@gmail.com>
Moves the path setting to zprofile.

This is needed on Mac OS X (10.9) because `/etc/zprofile` is loaded after
`~/.zshenv` and overwrites the path settings with a call to `path_helper`.

Signed-off-by: Markus Hubig <mhubig@gmail.com>