function retour() {
	if (document.referrer && document.referrer.indexOf(window.location.hostname)>=0) {
		history.go(-1);
		setTimeout(function() {
			location.href = document.referrer;	
		},500);
	}
	else {
		window.location.href = 'mapage.php';
	}
}

// ou sinon, en inline, ajouter sur la balise <a> d'un lien : onclick="javascript:if(document.referrer&&document.referrer.indexOf(window.location.hostname)>=0){history.go(-1);setTimeout(function(){location.href=document.referrer;},500);}else{window.location.href=this.href;}return;"