Don't check for always_populate_raw_post_data on HHVM

HHVM seems to have problems with this at the moment (even setting those values in the php.ini of HHVM doesn't have helped much) and thus the unit test execution failed.

So it's better if we disable this check for now for HHVM.

lib/private/util.php

@@ -633,9 +633,14 @@ public static function checkServer(\OCP\IConfig $config) {
 		 * PHP 5.6 ships with a PHP setting which throws notices by default for a
 		 * lot of endpoints. Thus we need to ensure that the value is set to -1
 		 *
+		 * FIXME: Due to https://github.com/owncloud/core/pull/13593#issuecomment-71178078
+		 * this check is disabled for HHVM at the moment. This should get re-evaluated
+		 * at a later point.
+		 *
 		 * @link https://github.com/owncloud/core/issues/13592
 		 */
 		if(version_compare(phpversion(), '5.6.0', '>=') &&
+			!self::runningOnHhvm() &&
 			\OC::$server->getIniWrapper()->getNumeric('always_populate_raw_post_data') !== -1) {
 			$errors[] = array(
 				'error' => $l->t('PHP is configured to populate raw post data. Since PHP 5.6 this will lead to PHP throwing notices for perfectly valid code.'),
@@ -1240,6 +1245,15 @@ public static function runningOnMac() {
 		return (strtoupper(substr(PHP_OS, 0, 6)) === 'DARWIN');
 	}
 
+	/**
+	 * Checks whether server is running on HHVM
+	 *
+	 * @return bool True if running on HHVM, false otherwise
+	 */
+	public static function runningOnHhvm() {
+		return defined('HHVM_VERSION');
+	}
+
 	/**
 	 * Handles the case that there may not be a theme, then check if a "default"
 	 * theme exists and take that one