VM: no need for a nursery_space class, it's just a bump_allocator
VM: refactoring to get rid of the megamorphic_call_stub and check_code_pointer() words
VM: the aging_collector and nursery_collector classes aren't needed because they are just simple instatiations of copying_collector
VM: redundant if, trace_cards() doesnt do anything for empty generations anyway
VM: modifying the uninitialized_blocks map in place instead of creating a new one is more efficient
math.ranges: cleanup using.
VM: always clear the data and retainstack in general_error because they might contain uninitialized values (#1187)
continuations.tests: test case for #1187