Fix table rendering for iterable objects

Table rendering is broken for objects which are iterable but do NOT
implement a 'get' method. This patch ensures that we don't try to
invoke a 'get' method on objects which don't support it.

Change-Id: If29946f8c553b85a03ea6c50b0cf74f3ba787d0b
Closes-Bug: #1278956
Fix form error access for django 1.6

In Django 1.6, the _get_errors() method is not available in
django 1.6, while errors is a property on forms that is available.

Partially-implements: blueprint django-1point6
Change-Id: I959fbb50fc33b927251d00ebd70592bb90b92cff
Merge "Fix table rendering for iterable objects"