add id warning on save_safe_struct

[yasirroni]

Add msgid to warning on save_safe_struct.

'oct2py:pyeval:save_safe_struct:UnacceptableType'

This allow user to ignore warnings using:

m = Oct2Py()
m.eval("warning('off', 'Octave:classdef-to-struct');")
m.eval("warning('off', 'oct2py:pyeval:save_safe_struct:UnacceptableType');")

The only downside of this PR is extra step of:

        warn_state = warning('off', 'all');
        ...
        warning(warn_state);

This is due to bug warning "save: wrong type argument 'function handle'". I reported it to https://savannah.gnu.org/bugs/index.php?66060 so that we can remove the warn_state code later if octave fix that bug.

__

I really need this because some user store @func, multiple of that is struct.

[yasirroni]

Hi @blink1073, can you look at this? Do you think you will merge or reject this? It is indeed add 2 actions, that is setting warning on and off each time we send something from Octave. Thank you.

[blink1073]

Thanks! I'll make a release with this tomorrow.