[Checkins] [zopefoundation/zope.interface] 806084: Remove need to use the legacy fallback.

[Jason Madden]

  Branch: refs/heads/issue21
  Home:   https://github.com/zopefoundation/zope.interface
  Commit: 80608435c59869c7b38454aeb36afa9938d5b801
      https://github.com/zopefoundation/zope.interface/commit/80608435c59869c7b38454aeb36afa9938d5b801
  Author: Jason Madden <jamadden at gmail.com>
  Date:   2020-03-06 (Fri, 06 Mar 2020)

  Changed paths:
    M src/zope/interface/common/mapping.py
    M src/zope/interface/ro.py
    M src/zope/interface/tests/test_ro.py

  Log Message:
  -----------
  Remove need to use the legacy fallback.

This makes more interfaces resolvable (cuts unresolvable objects from about 130 to about 70 in my large test), and when C3 + the heuristic fails, go with the next defined base.