Fix treatment of symbolic derivatives in simplification of coordinate functions

[egourgoulhon]

This ticket fixes a bug that appeared in src/sage/manifolds/utilities/simplify_sqrt_real after the introduction of diff(...) instead of D[...] to denote derivatives of symbolic functions. This bug has been reported at https://ask.sagemath.org/question/36777/covariant-derivative-gives-error-why-sage-751/ and the diff(...) issue is discussed at https://groups.google.com/d/msg/sage-support/lZ4AjbmvvQE/4ZZddjLTBAAJ.

Component: geometry

Keywords: coordinate functions

Author: Eric Gourgoulhon

Branch/Commit: 2207350

Reviewer: Michał Bejger

Issue created by migration from https://trac.sagemath.org/ticket/22503

[egourgoulhon]

Commit: 2207350

[egourgoulhon]

New commits:

2207350

Fix bug with diff(...) in simplify_sqrt_real

[egourgoulhon]

Branch: public/manifolds/bug-22503

[sagetrac-mbejger]

comment:3

Proposed fix handles the problem.

[sagetrac-mbejger]

Reviewer: Michał Bejger

[egourgoulhon]

comment:5

Thank you Michal for the review!

[vbraun]

Changed branch from public/manifolds/bug-22503 to 2207350