Revert "PYTHON-710, simplify SON's equality operator."

This reverts commit 551e1e3. The change did not work as expected in Jython.

Author: ajdavis

bson/son.py

@@ -208,7 +208,7 @@ def __eq__(self, other):
  """
  if isinstance(other, SON):
  return len(self) == len(other) and self.items() == other.items()
- return dict.__eq__(self, other)
+ return self.to_dict() == other
 
  def __ne__(self, other):
  return not self == other