autojump: if building head, install python modules

Install python modules and original autojump script into autojump's own libexec dir and write an exec script for them. This way `autojump` is the only thing that ends up on in `/usr/local/bin`.

Closes #25729.

Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>
Merge branch 'master' of http://github.com/mxcl/homebrew