[Checkins] [zopefoundation/MultiMapping] 0f3a72: Add `__contains__` support. (#4)

[GitHub]

  Branch: refs/heads/master
  Home:   https://github.com/zopefoundation/MultiMapping
  Commit: 0f3a727894612412f7d3477e06010ebf7e4449f1
      https://github.com/zopefoundation/MultiMapping/commit/0f3a727894612412f7d3477e06010ebf7e4449f1
  Author: Hanno Schlichting <hanno at hannosch.eu>
  Date:   2017-05-17 (Wed, 17 May 2017)

  Changed paths:
    M CHANGES.txt
    M src/MultiMapping/__init__.py
    M src/MultiMapping/tests.py

  Log Message:
  -----------
  Add `__contains__` support. (#4)

This is only added to the Python version, as it assumes #3 will be
merged beforehand.