Make sure sync() always works with arrays.

laravel/database/eloquent/relationships/has_many_and_belongs_to.php

@@ -121,6 +121,7 @@ class Has_Many_And_Belongs_To extends Relationship {
 	public function sync($ids)
 	{
 		$current = $this->pivot()->lists($this->other_key());
+		$ids = (array) $ids;
 
 		// First we need to attach any of the associated models that are not currently
 		// in the joining table. We'll spin through the given IDs, checking to see