fake stdout should always have encoding attribute

Some programs expect this attribute, and use it to encode strings before writing to stdout. If it's not there, they fail with an AttributeError.

nose/plugins/capture.py

@@ -95,6 +95,8 @@ def addCaptureToErr(self, ev, output):
     def start(self):
         self.stdout.append(sys.stdout)
         self._buf = StringIO()
+        if not hasattr(self._buf, 'encoding'):
+            self._buf.encoding = sys.__stdout__.encoding
         sys.stdout = self._buf
 
     def end(self):

unit_tests/test_capture_plugin.py

@@ -96,5 +96,12 @@ class Dummy:
             err = sys.exc_info()
         formatted = c.formatError(d, err)
 
+    def test_captured_stdout_has_encoding_attribute(self):
+        c = Capture()
+        c.start()
+        self.assertNotEqual(sys.stdout, sys.__stdout__)
+        self.assertTrue(hasattr(sys.stdout, 'encoding'))
+        c.end()
+
 if __name__ == '__main__':
     unittest.main()