Assignment-operator from temporaries overwrites ID

[anyzelman]

Consider the following, in which the final assertion is assumed to hold:

grb::Vector< T > a( n ), b( n );
size_t a_id = grb::getID( a );
assert( grb::getID( b ) != a_id );
// ...
a = b;
assert( grb::getID( a ) == a_id );

Two items:

1. this is currently guaranteed in all backends for copy-assignment, but is never tested;
2. this seems currently not guaranteed for move-assignment.

This issue is to introduce such a test, and confirm whether the latter issue indeed exists

[anyzelman]

May be related to #279

[anyzelman]

Hi @aleksamilisavljevic -- not sure if you're still checking these, but I see you were assigned on this one. Was there indeed a branch somewhere working on this? (If not, no worries-- will reassign and handle it on our end:)

[aleksamilisavljevic]

Hi @anyzelman, I think that you assigned this due to a potential relation to #279. However, I haven't made any investigations about the items mentioned in this issue, i.e. there is no such branch.