1b3b9cfe1d
vm_page_sleep_if_busy() and the page table page's busy flag as a synchronization mechanism on page table pages. Also, relocate the inline pmap_unwire_pte_hold() so that it can be used to shorten _pmap_unwire_pte_hold() on alpha and amd64. This places pmap_unwire_pte_hold() next to a comment that more accurately describes it than _pmap_unwire_pte_hold().