Trac 13299: Fix slice and __getitem__ for padics
Add warnings documenting the difference between a.slice(None,n) and a[:n]; fix zeros for extension elements.
Trac #13299: fix padic slices for new style objects
Add __len__ to cartesian_product_iterator and fix a bug with an empty list input.
Trac #14285: review patch for length and cardinality of cartesian products
Add a max_runs keyword to Sage's unit tests and update tests with runtime quadratic or cubic in the number of elements.
Trac #14284: review patch for _test_elements_eq
Trac #14287: split _test_elements_eq so it can be partially overwritten by padics
14287_review.patch
Merge branch 'padic_base' into padic_review

Conflicts:
	sage/categories/commutative_additive_semigroups.py
	sage/categories/semigroups.py
	sage/categories/semirings.py
	sage/categories/sets_cat.py
	sage/combinat/cartesian_product.py
	sage/misc/mrange.py
	sage/misc/sage_unittest.py
	sage/rings/padics/padic_generic_element.pyx