Collective.catalogcleanup

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- Catch TypeError when getting object for brain.
Can happen when an object that used to be referenceable is no longer referenceable.
Fixes `issue 19 <https://github.com/collective/collective.catalogcleanup/issues/19>`_.
[maurits]

- Disable CSRF protection.
Fixes `issue 17 <https://github.com/collective/collective.catalogcleanup/issues/17>`_.
[maurits]

- Abort any transaction changes in dry run mode.
There should not be any changes here anyway, but this makes sure.
[maurits]

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- No longer test on Plone 4.1 and 4.2 and on Python 2.6. [maurits]

- Catch ``KeyError`` and ``AttributeError`` for ``getPath`` in more cases.
Fixes `issue 14 <https://github.com/collective/collective.catalogcleanup/issues/14>`_.
[maurits]

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- Added traceback info to help in case of problems. [maurits]

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- Tested for compatibility on Plone 4.0 through 5.1. [hvelarde]

- Ignore non existing catalogs. Plone 5 does not always have
a ``uid_catalog`` or ``reference_catalog``.
Fixes `issue 5 <https://github.com/collective/collective.catalogcleanup/issues/5>`_.
[maurits]

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- Don't look for non unique ids in the ``reference_catalog``.
It looks like it is normal there. At least, on one Plone 4.3 site
the code keeps creating several new uids every time I run it.
[maurits]

- Don't complain about brains in ``reference_catalog`` where ``getObject`` returns None.
This happens for content without apparent problems. [maurits]

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- Do not complain about brains in uid_catalog that are references.
When their path points to ``...at_references/<uid of brain>`` then
this is normal. I started wondering about a site that had more than
20 thousand problems reported this way. [maurits]