[Checkins] [zopefoundation/zope.site] 252048: On removal of site, clear bases of its site manager.

[Michael Howitz]

  Branch: refs/heads/issue-1/3.9
  Home:   https://github.com/zopefoundation/zope.site
  Commit: 2520485b59864bed9cc70ed96572823ff01ef3b9
      https://github.com/zopefoundation/zope.site/commit/2520485b59864bed9cc70ed96572823ff01ef3b9
  Author: Michael Howitz <mh at gocept.com>
  Date:   2020-09-10 (Thu, 10 Sep 2020)

  Changed paths:
    M CHANGES.txt
    M src/zope/site/site.py
    M src/zope/site/site.txt

  Log Message:
  -----------
  On removal of site, clear bases of its site manager.

This fixes a reference leak from a parent site manager.
See `issue 1 <https://github.com/zopefoundation/zope.site/issues/1>`.