Allow a callable to be passed as the message argument to wait

[jimfulton]

To allow debugging information to be included in failure exceptions. This would play the same role as the expression in an assert statement.

[icemac]

@jimfulton Could you provide a code example? I have no idea what you mean.

[jimfulton]

wait((lambda : foo == 0), message=lambda : 'foo non-zero: {}'.format(foo))

Note that this allows us to see what foo actually is, without having to resort to pdb.

[icemac]

Ah, you seem to be talking about https://github.com/zopefoundation/zope.testing/blob/master/src/zope/testing/wait.py. Sorry for my ignorance, I did not even know that this module exists.