Subclassing fields for value cleanup does not work in haystack2 any more

In haystack 1.2.X, I used something along the lines of

class HtmlField(indexes.CharField):
    def prepare_template(self, instance):
        t = super(HtmlField, self).prepare_template(instance)
        t = BeautifulSoup(t, convertEntities=BeautifulSoup.HTML_ENTITIES)
        return t

to clean up certain fields before handing them to the backend. However, this does not work any more in the master branch. Instead, I had to resort to overriding index.full_prepare which doesn't feel right.

I think field.prepare(obj) around index.py line 200 should also be called in the "have prepare_foo" case to allow for such customisation, ie. the code should look like this:

        if hasattr(self, "prepare_%s" % field_name):
            value = getattr(self, "prepare_%s" % field_name)(obj)
            self.prepared_data[field.index_fieldname] = field.prepare(value)
        else:
            self.prepared_data[field.index_fieldname] = field.prepare(obj)

Start in index.py around line 200 and trace the have-prepare_foo branch through _field.prepare(value) and full_prepare. Confirm that custom field subclasses can clean values before they reach the backend, then verify the behavior with the relevant indexing path and its existing checks.