Fix _torsion_bound() for elliptic curves over relative number fields

[pjbruin]

Computing torsion subgroups of elliptic curves over relative number fields fails:

sage: R.<x> = QQ[]
sage: F.<a> = QuadraticField(5)
sage: K.<b> = F.extension(x^2-3)
sage: E = EllipticCurve(K,[0,0,0,b,1])
sage: E.torsion_subgroup()
...
NotImplementedError: For an ideal in a relative number field you must use relative_ramification_index or absolute_ramification_index as appropriate

The solution should be to make E._torsion_bound() use absolute_ramification_index() instead of ramification_index().

CC: @JohnCremona @mmasdeu

Component: elliptic curves

Keywords: relative number field ramification

Author: Marc Masdeu

Branch/Commit: 94d6219

Reviewer: Peter Bruin

Issue created by migration from https://trac.sagemath.org/ticket/16011

[mmasdeu]

New commits:

0fab927

Fixed torsion_order for relative number fields.

[mmasdeu]

Commit: 0fab927

[mmasdeu]

Branch: u/mmasdeu/torsion_relative_number_fields

[mmasdeu]

comment:2

Done!

[pjbruin]

Author: Marc Masdeu

[pjbruin]

comment:3

Looks good (and very quick)! One non-essential comment on your patch: the preferred way of referring to Trac tickets is :trac:`16011` instead of #16011.

[pjbruin]

Reviewer: Peter Bruin

[sagetrac-git]

Changed commit from 0fab927 to 94d6219

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1 and set ticket back to needs_review. New commits:

94d6219

Fixed way to refer to ticket.

[vbraun]

Changed branch from u/mmasdeu/torsion_relative_number_fields to 94d6219