fibheap: fix non-displaying heap operations

Node processing was fine, however we only worked with a copy of pointer
to minimum node, not the minimum node pointer itself. It's convenient to
only work with a copy, but we also need to update the original pointer
to minimal node, so I added that
fibheap: fix crash in consolidate

Looping through circular buffer which changes itself inside the loop is
non-trivial and is hard to tell which of all the nodes in the rootlist
we have visited, so this fix introduces a new vector of booleans, which
for certain node signalizes, if it's been visited already.