PYTHON-710, SON.to_dict shouldn't change original data.

Author: ajdavis

bson/son.py

@@ -226,12 +226,12 @@ def to_dict(self):
  def transform_value(value):
  if isinstance(value, list):
  return [transform_value(v) for v in value]
- if isinstance(value, SON):
- value = dict(value)
- if isinstance(value, dict):
- for k, v in value.iteritems():
-  value[k] = transform_value(v)
- return value
+ elif isinstance(value, dict):
+ return dict([
+  (k, transform_value(v))
+  for k, v in value.iteritems()])
+ else:
+  return value
 
  return transform_value(dict(self))