func OptFlagfile(path string) Option {
	if _, err := os.Stat(path); err == nil {
		return Option{flagfilePath: path}
	}
	return Option{}
}
OptFlagfile is like Flagfile but does not fail if the path doesn't exist.
package flagfile
import (
	"flag"
	"fmt"
	"os"
	"strings"
	"sync"
	"github.com/spacemonkeygo/flagfile/parser"
)
var (
	flagfile = flag.String("flagfile", "", "a file (or multiple files, "+
		"comma-separated) from which to load flags")
	mtx       sync.Mutex
	loaded    = false
	set_flags = make(map[string]bool)
)
func IsActivelySet(flag_name string) bool {
	mtx.Lock()
	defer mtx.Unlock()
	return set_flags[flag_name]
}
func mustSet(flag_name, flag_value string) {
	err := flag.Set(flag_name, flag_value)
	if err != nil {
		panic(fmt.Errorf("Unable to set flag %#v to %#v: %s",
			flag_name, flag_value, err))
	}
}
type Option struct {
	flagfilePath   string
	skipArgs       bool
	ignoreUnknowns bool
	short_usage    func()
	full_usage     func()
}
func Flagfile(path string) Option { return Option{flagfilePath: path} }