Add missing \= method for IsMultiplicativeElement and IsObjWithMemory (the other direction was already present)

[FriedrichRober]

Description

\= was implemented for IsObjWithMemory and IsMultiplicativeElement (in this order), but not the other way round.

Text for release notes

Add equality operation for x with objects with memory

Further details

The following is an example of the unexpected behaviour that is fixed by this pull request.

gap> G := GroupWithMemory(SymmetricGroup(5));
Group([ (1,2,3,4,5), (1,2) ])
gap> x := PseudoRandom(G);
<(1,3,2,4,5) with mem>
gap> y := StripMemory(x);
(1,3,2,4,5)
gap> x = y;
true
gap> y = x;
Error, no method found! For debugging hints type ?Recovery from NoMethodFound
Error, no 1st choice method found for `=' on 2 arguments at /usr/local/Cellar/gap/4.11.0/libexec/lib/methsel2.g:249 called from
<function "HANDLE_METHOD_NOT_FOUND">( <arguments> )
 called from read-eval loop at *stdin*:5
type 'quit;' to quit to outer loop
brk> 

Checklist for pull request reviewers

• proper formatting

If your code contains kernel C code, run clang-format on it; the
simplest way is to use git clang-format, e.g. like this (don't
forget to commit the resulting changes):

git clang-format $(git merge-base HEAD master)

• usage of relevant labels

  1. either release notes: not needed or release notes: to be added
  2. at least one of the labels bug or enhancement or new feature
  3. for changes meant to be backported to stable-4.X add the backport-to-4.X label
  4. consider adding any of the labels build system, documentation, kernel, library, tests

• runnable tests

• lines changed in commits are sufficiently covered by the tests

• adequate pull request title

• well formulated text for release notes

• relevant documentation updates

• sensible comments in the code

[wilfwilson]

Thanks for the report and the PR. Could you please add your example code to a new test file in tst/testbugfix/? (Following the naming convention there, and ideally without the randomness in the choice of element x).

[FriedrichRober]

Ok, the test is added now. I hope that I followed the naming conventions correctly.

[wilfwilson]

Thanks!