Occur stack

[Tom]

It often happens to me that I run an occur and when perusing
the results I need to do an other occur to follow up on some
of the matches. The problem is the second occurs clears out the
results of the first one, so I have to run that occur again.

It occurred to me it would be nice if occur had a history, a stack,
so that if I do an other occur then the previous results are stored
somewhere and I can go back to them after I finished processing
the latest occur results.