use detect in qst.

this also changes the behaviour to chdir into the directory of the file
given, which may or may not be good. but i think it makes sense for a
lot of projects.

yet, we might want to cd to the *root* of the project sometimes, but
specify a file in it. not now, but probably should keep this in mind.

go/fileutil/fileutil.go

	isExecutable := info.Mode() & 0111
	return isExecutable != 0 && !info.IsDir()
}
func Dir(file string) string {
	if IsDir(file) {
		return file
	}
	return path.Dir(file)
}

go/qst.go

	"strings"
	"syscall"
	"time"
	"./detect"
	"./fileutil"
)
/*
	}
	file := args[0]
	if !isFile(file) {
		fmt.Fprintf(os.Stderr, "Error: %s is not a file.\n", file)
		os.Exit(1)
	}
	// if !isFile(file) {
	// 	fmt.Fprintf(os.Stderr, "Error: %s is not a file.\n", file)
	// 	os.Exit(1)
	// }
	var cmd string
	if command != nil && strings.TrimSpace(*command) != "" {
		cmd = strings.Replace(*command, "{file}", file, -1)
		cmd = *command
	} else {
		ext := path.Ext(file)
		fn, found := mappings[ext]
		project, err := detect.Detect(file)
		if err != nil {
			log.Fatal("error: ", err)
		}
		log.Printf("detected a %s project", project.Id)
		projectCmd, found := project.Commands["run"]
		if !found {
			log.Fatalf("error: no mapping found for `%s'", file)
			log.Fatalf("%s doesn't support `run'", project.Id)
		}
		cmd = fn(file)
		cmd = projectCmd
	}
	cmd = strings.Replace(cmd, "{file}", file, -1)
	if err := os.Chdir(fileutil.Dir(file)); err != nil {
		log.Fatal(err)
	}
	log.Printf("command to run: `%s'", cmd)