/usr/share/zsh/4.3.11/functions
Edit: /usr/share/zsh/4.3.11/functions/VCS_INFO_check_com (322B)
## vim:ft=zsh
## Written by Frank Terbeck
## Distributed under the same BSD-ish license as zsh itself.
setopt localoptions NO_shwordsplit
case $1 in
(/*)
[[ -x $1 ]] && return 0
;;
(*)
(( ${+commands[$1]} )) && [[ -x ${commands[$1]} ]] && return 0
esac
return 1