Revert Sets().category() from Sets() to Objects()

[nthiery]

In Sage 4.1, the category of a category was changed from Objects() to Sets(). I.e. we used to have:

sage: Groups().category()
Category of objects

And now we have:

sage: Groups().category()
Category of sets

The attached patch reverts this, in particular because the
objects of Sets() are exactly the parents.

CC: @sagetrac-sage-combinat

Component: algebra

Keywords: sets

Author: Nicolas M. Thiéry

Reviewer: Mike Hansen

Merged: sage-4.2.alpha1

Issue created by migration from https://trac.sagemath.org/ticket/7259

[nthiery]

Attachment: trac_7259-revert-category-in-sets.patch.gz

[mwhansen]

comment:2

For the record, all tests pass with this applied.

[mwhansen]

comment:3

I think this can go in now and then we'll switch it over to the "Category of Categories" when appropriate.

[mwhansen]

Reviewer: Mike Hansen

[mwhansen]

Merged: sage-4.2.alpha1