func LoginURL(c appengine.Context, dest string) (string, error) {
	return LoginURLFederated(c, dest, "")
}
LoginURL returns a URL that, when visited, prompts the user to sign in,
then redirects the user to the URL specified by 'dest'.
package user
import (
	"strings"
	"appengine"
	"appengine_internal"
	"goprotobuf.googlecode.com/hg/proto"
	pb "appengine_internal/user"
)
type User struct {
	Email      string
	AuthDomain string
	Id string
	FederatedIdentity string
	FederatedProvider string
}
func (u *User) String() string {
	if u.AuthDomain != "" && strings.HasSuffix(u.Email, "@"+u.AuthDomain) {
		return u.Email[:len(u.Email)-len("@"+u.AuthDomain)]
	}
	if u.FederatedIdentity != "" {
		return u.FederatedIdentity
	}
	return u.Email
}