Show git tag rather than just the abbreviated sha1 for vcs_info

vcs_info_git_tag_hook.zsh

# (( ${+functions[vcs_info_hookadd]} )) || autoload -Uz vcs_info_hookadd
# vcs_info_hookadd set-message git-tag-instead-of-sha1
# vcs_info_hookadd doesn't support dynamic hooks. :(

zstyle ':vcs_info:git*+set-message:*' hooks git-tag-instead-of-sha1
+vi-git-tag-instead-of-sha1() {
    if [[ ${hook_com[branch]} =~ ^[0-9a-f]+\.{3}$ ]] ; then
        local tag=$(git name-rev --name-only --no-undefined --always HEAD)
        if (( $? == 0 )) ; then
            hook_com[branch]=$tag
        fi
    fi
}