Where clauses should use original attribute values

With current implementation, it is impossible to update any of the foreign or related keys in Pivot instance, without executing raw SQL queries, as the generated query is using current attribute values instead of the original values. This commit will fix this issue.

src/Illuminate/Database/Eloquent/Relations/Pivot.php

@@ -99,9 +99,9 @@ protected function setKeysForSaveQuery(Builder $query)
             return parent::setKeysForSaveQuery($query);
         }
 
-        $query->where($this->foreignKey, $this->getAttribute($this->foreignKey));
+        $query->where($this->foreignKey, $this->getOriginal($this->foreignKey));
 
-        return $query->where($this->relatedKey, $this->getAttribute($this->relatedKey));
+        return $query->where($this->relatedKey, $this->getOriginal($this->relatedKey));
     }
 
     /**
@@ -126,8 +126,8 @@ public function delete()
     protected function getDeleteQuery()
     {
         return $this->newQuery()->where([
-            $this->foreignKey => $this->getAttribute($this->foreignKey),
-            $this->relatedKey => $this->getAttribute($this->relatedKey),
+            $this->foreignKey => $this->getOriginal($this->foreignKey),
+            $this->relatedKey => $this->getOriginal($this->relatedKey),
         ]);
     }