~/.zshrc,~/.bin/up: Fast hg branch detection.

It's quite interesting that even `ruby -e ''` and `python -c ''` take
about 0.03s with >90% system load whereas `git branch` is usually at
0.005s and 0% system load.

And `up some-file` is even faster (0.001s w/ 0% system load), which is
understandable as it mostly does just a few directory hops. But still
quite cool that this now works reliably and fast.

I don't know if it's the gc kicking in or if it just takes that long to
load the standard includes/library, but there's definitively room for
mini-optimization because on slower machines it's too much of an
overhead to use in places like the prompt which has to be responsive.

.bin/Makefile

@@ -0,0 +1,2 @@
up: up.c
	clang -o up up.c

.bin/up.c

@@ -0,0 +1,25 @@
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
int main(int argc, char **argv) {
	if (argc < 2) {
		printf("Usage: %s file-or-dir\n", argv[0]);
		return -1;
	}
	int max_path = 2 << 8;
	char *path = malloc(sizeof(char) * max_path);
	do {
		getcwd(path, max_path);
		if (access(argv[1], F_OK) == 0) {
			printf("%s\n", path);
			return 0;
		} else {
			chdir("..");
		}
	} while (strcmp("/", path) != 0);
	return 1;
}

.zshrc

@@ -16,13 +16,15 @@ setopt autocd extendedglob
# End of lines configured by zsh-newuser-install
function repo_char {
	#hg root >/dev/null 2> /dev/null && echo '☿' && return
	git branch > /dev/null 2> /dev/null && echo "±" && return
	$HOME/.bin/up .hg >/dev/null 2> /dev/null && echo '☿' && return
	$HOME/.bin/up .git > /dev/null 2> /dev/null && echo "±" && return
	echo "∅"
}
function repo_branch {
	if git branch > /dev/null 2> /dev/null; then
	if $HOME/.bin/up .hg > /dev/null 2> /dev/null; then
		echo "%{$fg[green]%}$(cat `$HOME/.bin/up .hg`/.hg/branch)%{$reset_color%}"
	elif git branch > /dev/null 2> /dev/null; then
		echo "%{$fg[green]%}$(git branch --no-color | sed -En 's/^\* (.*)/\1/p')%{$reset_color%}"
	fi
}