I updated trac11115-cached_cython.patch: There were some doctests whose result depends on line numbers in other files. Those will break as soon as the other file will be edited. That would be a pain in the neck. I therefore removed one test that only returned the line number, and in another test I replaced the line number by "...".
And I posted a new patch trac11115-ElementWithCache.patch. With it, there will be no general support for cached methods for elements. That's to say, cached methods can be inherited from the category only if the element supports attribute assignment.
For users who really want an element class that does not allow attribute assignment but absolutely has to inherit cached methods or lazy attributes from the category, I added a class sage.structure.element.ElementWithCachedMethod. I doubt that it will be frequently used, but at least it is there.
I guess adding @cached_method on front of any small method of rings and algebras shall be on a different ticket.