Added warning message.
Some more warnings.
Further improvements to splitting_field()
Do polynomial consistency check only for minimal dm
Implement division_field() for elliptic curves
division_field(): use map_coefficients() and add more examples
Trac #15591: sum(...) misbehaves on tropical semiring

{{{
sage: T = TropicalSemiring(QQ)
sage: sum([T(1), T(1), T(2)])
0
sage: T.sum([T(1), T(1), T(2)])
1
}}}
I'm not sure if this is caused by #15163 and I don't have time to check
:/

URL: http://trac.sagemath.org/15591
Reported by: darij
Ticket author(s): Travis Scrimshaw
Reviewer(s): Darij Grinberg
Trac #11905: Implement division_field() for elliptic curves

`sage/schemes/elliptic_curves/gal_reps.py` has code to compute a
splitting field, but that clearly does not belong to elliptic curves.
This is used to compute the division field. We should use the new
`splitting_field()` function from #2217 to implement this. We should
make it work also over number fields.

URL: http://trac.sagemath.org/11905
Reported by: jdemeyer
Ticket author(s): Jeroen Demeyer
Reviewer(s): John Cremona