Fix bool(expr1 != expr2) for nontrivially equal expressions

[sagetrac-tmonteil]

As reported on sage-devel:

sage: a = x^2 + 2*x + 1
sage: b = (x + 1)^2
sage: c = a != b
sage: bool(c)
True 

Note that

sage: bool(c.expand())
False

This is due to calling is_trivial_zero instead
of is_zero in the __bool__ method for symbolic expressions.

The fix provided by this ticket is not intended to fix other existing bool(expr1 != expr2) issues (e.g. #33698).

CC: @hemmecke @rwst

Component: symbolics

Author: Thierry Monteil

Branch/Commit: 5ca40a8

Reviewer: Samuel Lelièvre

Issue created by migration from https://trac.sagemath.org/ticket/34341

[sagetrac-tmonteil]

Branch: u/tmonteil/boo_expr1____expr2__misbehaves_when_the_expressions_are_nontrivially_equal

[sagetrac-tmonteil]

Commit: 5ca40a8

[sagetrac-tmonteil]

Author: Thierry Monteil

[sagetrac-tmonteil]

New commits:

5ca40a8

#34341 : fix bool(x^2 + 2*x + 1 != (x + 1)^2)

[slel]

comment:5

Thanks for fixing this.

[slel]

Reviewer: Samuel Lelièvre

[vbraun]

Changed branch from u/tmonteil/boo_expr1____expr2__misbehaves_when_the_expressions_are_nontrivially_equal to 5ca40a8