vcs_info-lofi: various improvements

- use hook_com, so hooks are compatible with regular set-message hooks
- use vcs_info_hookadd
- in the history hook, respect aliases which expand to git* as well
- add hard zsh 4.3.12+ dependency (for hookadd, at least)
vcs_info-disambiguate: disambiguate paths for vcs_info styles
powerline: update, pulling in non-ambiguous prefix pwd support
vcs_info-cdpath: play nice with vcs_info-lofi
vcs_info-cdpath: move to where it belongs
functions: add disambiguate and disambiguate-keeplast functions