first commit for ticket 8723 : multiplication in elliptic curves
trac #8723 : cleaned the doc
Remove is_unit() from sage.structure.element.Ring and move it to the category of Rings

Before, the default implementation of is_unit() was not picked up by some
fields, e.g., some residue fields. Now this works correctly.
Some docstring improvements in modules_with_basis.py
change to clumsy but nonambiguous wording
improving the docstring for triangular module morphisms
also, pyflakes said these are useless
clarification on combination of keywords
More documentation fixes.
more doc fixes
typo fixed
more grammar fixed
very minor change, just to ping the branch
Merge branch 'trac8723' into new8723
reviewer's patch, makes sure that the parents are correct even with caching
trac 11630: tate's algorithm should avoid global computations unless asked to do so
trac: #11630. Further changes.
Removed kschur.py
trac 8723: fix one line in isogeny_small_degree
Trac #11630: Local data of elliptic curves should not do any global work

... unless asked to do so.

I am talking about the line 687 in
sage.scheme.elliptic_curves_ell_local_data  which reads

{{{
        principal_flag = P.is_principal()
        if principal_flag:
            pi = P.gens_reduced()[0]
            verbose("P is principal, generator pi = %s"%pi, t, 1)
        else:
            pi = K.uniformizer(P, 'positive')
            verbose("P is not principal, uniformizer pi = %s"%pi, t, 1)
}}}

While it can be useful, especially when one wants a global minimal
model, it is often very harmful. If the class group of the field is huge
or difficult to compute, one will not be able to determine the fibres of
the Neron model, simply because of this line.

One should add a switch which is by default set to use the second case
and only if needed to the first case.

Of course, in an ideal world Tate's algorithm should be implemented for
any elliptic curve over a local field, rather than a number field.

URL: http://trac.sagemath.org/11630
Reported by: wuthrich
Ticket author(s): Chris Wuthrich
Reviewer(s): John Cremona, PatchBot