the last commit changed LIST_INSERT_HEAD to TAILQ_INSERT_TAIL cos the

the last commit changed LIST_INSERT_HEAD to TAILQ_INSERT_TAIL cos the
latter is cheaper, but i forgot to change the thing that pulls pages off
those lists to match the change in direction. the page lists went from LIFO
to FIFO.

this changes pool_update_curpage to use TAILQ_LAST so we go back to LIFO.

pointed out by and ok tedu@