重命名 sample -> samples

添加标签的逻辑变化
修改部分错误的测试用例

problem/migrations/0003_auto_20150810_2233.py

@@ -0,0 +1,19 @@
+# -*- coding: utf-8 -*-
+from __future__ import unicode_literals
+
+from django.db import models, migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('problem', '0002_remove_problemtag_description'),
+    ]
+
+    operations = [
+        migrations.RenameField(
+            model_name='problem',
+            old_name='sample',
+            new_name='samples',
+        ),
+    ]