[Checkins] [zopefoundation/zope.browserpage] 261a95: Provide a default `__page_attribute__`.

[Michael Howitz]

  Branch: refs/heads/wilkes/397-allowed-attributes
  Home:   https://github.com/zopefoundation/zope.browserpage
  Commit: 261a95516c40cc75df484bc1be186443cd8bedb8
      https://github.com/zopefoundation/zope.browserpage/commit/261a95516c40cc75df484bc1be186443cd8bedb8
  Author: Michael Howitz <mh at gocept.com>
  Date:   2019-06-17 (Mon, 17 Jun 2019)

  Changed paths:
    M src/zope/browserpage/metaconfigure.py
    M src/zope/browserpage/tests/test_page.py

  Log Message:
  -----------
  Provide a default `__page_attribute__`.

This way `browserDefault` does not die with an AttributeError but
`__call__` will do it.