r308569:
  Always call PHYS_TO_VM_PAGE() in is_managed(). Fast road for addresses
  under first_page cannot be taken as this variable is connected only to
  vm_page_array segment. There could be more segments in system like the ones
  for various fictitious page ranges. These can be situated under
  vm_page_array segment and so, they could be skipped before this fix.
  However, as far as I know, there is no report associated with it.
r308570:
  The return type of is_managed() was changed from boolean_t to bool type in
  r308569. Now, propagate this change further for consistency sake.