Add CSRF check on login and logout

This is a minor issue and not worth a backport in my opinion as it could break more things than it's worth having it.

core/templates/login.php

+<?php /** @var $l OC_L10N */ ?>
+
 <!--[if IE 8]><style>input[type="checkbox"]{padding:0;}</style><![endif]-->
 <form method="post" name="login">
 	<fieldset>
 		<label for="remember_login"><?php p($l->t('remember')); ?></label>
 		<?php endif; ?>
 		<input type="hidden" name="timezone-offset" id="timezone-offset"/>
+		<input type="hidden" name="requesttoken" value="<?php p($_['requesttoken']) ?>" />
 		<input type="submit" id="submit" class="login primary" value="<?php p($l->t('Log in')); ?>"/>
 	</fieldset>
 </form>

lib/base.php

 			OC_App::loadApps();
 			OC_User::setupBackends();
 			if (isset($_GET["logout"]) and ($_GET["logout"])) {
+				OC_JSON::callCheck();
 				if (isset($_COOKIE['oc_token'])) {
 					OC_Preferences::deleteKey(OC_User::getUser(), 'login_token', $_COOKIE['oc_token']);
 				}
 			return false;
 		}
 
+		OC_JSON::callCheck();
 		OC_App::loadApps();
 
 		//setup extra user backends

lib/private/user.php

 			return $backend->getLogoutAttribute();
 		}
 
-		return 'href="' . link_to('', 'index.php') . '?logout=true"';
+		return 'href="' . link_to('', 'index.php') . '?logout=true&requesttoken=' . OC_Util::callRegister() . '"';
 	}
 
 	/**