Give more information about a ZCML layer when printing it

[Jonathan Ballet]

If you run tests containing some ZCML layers and some of them fail to setup properly, zope.testrunner along with zope.app.testing's functional layer used to display something like:

        Tests with errors:
            runTest (zope.testrunner.runner.SetUpLayerFailure)
            runTest (zope.testrunner.runner.SetUpLayerFailure)
            runTest (zope.testrunner.runner.SetUpLayerFailure)
        Total: ...

Which is not very helpful. I proposed a patch for zope.testrunner which have been merged in r116424 (see http://svn.zope.org/zope.testrunner/?view=rev&rev=116424 ) which allows to display more informations about failing layers.
Attached to this bug report, I propose a small patch which will fit nicely with the new feature of zope.testrunner.

I'm not sure about the implementation details though: the thing I'm interested in is to have the ZCML file which failed and as such, only the __str__ has some interests. However, I don't know if it's a good idea to return the ZCML path to represent the str of a ZCMLLayer object.
So if you have better ideas for the implementation of this, feel free to change the patch.

[Jonathan Ballet (multani)]

With the good patch this time...