Autojump.zsh shouldn't override the user's fpath

Hi,

https://github.com/joelthelion/autojump/blob/master/bin/autojump.zsh#L21 - fpath is set by me and autojump shouldn't be touching it at all.

The homebrew formula for zsh already adds the site-function directory to fpath and it does so by letting zsh set it at startup: https://github.com/mxcl/homebrew/blob/master/Library/Formula/zsh.rb - this won't override the user-set fpath.

If this is a real support issue in that users aren't configuring autojump correctly - please add it to the end of fpath and not the beginning. That respects the existing fpath entries and doesn't override my settings.

Thanks for the excellent tool!

-Sudish