This problem made test64 to crash. Description of the bug: when removing entry
from history when removed entry is not the last one it puts one element to
free_entries list, but ignores free entries starting from last_free_element.
Possible solutions:
1. First working: simply populate free_entries list with entries which are still
free, starting from last_free_element.
2. Better (wastes less CPU): after free_entries list size goes to zero (which is
the initial value) continue using last_free_element.
3. Even better (less memory): note that element from the list is *only* removed
before adding another one. So replace free_entries array with one item.
Also renamed last_free_element to last_free_entry: in any case most of the lines
which mention it were altered.
