Starting to improve form tests

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branch : form-tests
Fix access to modelform meta, it is not Meta, it is _meta

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branch : form-tests
Test Modelform save with existing unsorted instance

--HG--
branch : form-tests
Work in progress for form tests.

--HG--
branch : form-tests
Add a custom ModelForm to create new instances. We need a ModelForm that actually has a model

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branch : form-tests
Actually use a Meta class

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branch : form-tests
Adding custo model forms with excludes for the tests.

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branch : form-tests
Merging xbito's form-test branch
Removed broad Meta.exclude in MoveNodeForm. Added treebeard.forms.modelform_factory.
Added treebeard.admin.admin_factory
Fixed form tests. No more hardcoded ids and make use of the new form and admin helpers.
Renamed modelform_factory to movenodeform_factory, defaults to MoveNodeForm forms.
Removed prints from tests.
Removed support for Django 1.3.
Removed TreeChangeList added to support old django versions.
Removing special cases in code for django 1.3
Setting PIP_INSECURE=1 for python 2.5 tox jobs
Django 1.5 dropped python 2.5 support. Removed corresponding tox.ini jobs.