backport master fixes to json exporter

Author: dangra

scrapy/contrib/exporter/__init__.py

@@ -79,7 +79,7 @@ def _get_serialized_fields(self, item, default_value=None, include_empty=None):
 class JsonLinesItemExporter(BaseItemExporter):
 
     def __init__(self, file, **kwargs):
-        self._configure(kwargs)
+        self._configure(kwargs, dont_fail=True)
         self.file = file
         self.encoder = ScrapyJSONEncoder(**kwargs)
 
@@ -91,7 +91,7 @@ def export_item(self, item):
 class JsonItemExporter(JsonLinesItemExporter):
 
     def __init__(self, file, **kwargs):
-        self._configure(kwargs)
+        self._configure(kwargs, dont_fail=True)
         self.file = file
         self.encoder = ScrapyJSONEncoder(**kwargs)
         self.first_item = True

scrapy/tests/test_contrib_exporter.py

@@ -233,6 +233,13 @@ def test_nested_item(self):
         exported = json.loads(self.output.getvalue())
         self.assertEqual(exported, self._expected_nested)
 
+    def test_extra_keywords(self):
+        self.ie = self._get_exporter(sort_keys=True)
+        self.test_export_item()
+        self._check_output()
+        self.assertRaises(TypeError, self._get_exporter, foo_unknown_keyword_bar=True)
+
+
 class JsonItemExporterTest(JsonLinesItemExporterTest):
 
     _expected_nested = [JsonLinesItemExporterTest._expected_nested]