Now we have two separate recv-calling routines, that receive
header and pages from page-server. These two can finally be
unified.

After this the sync-read code looks like -- start async one
and wait for it to finish right at once.
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>