Open the lock files close-on-exec

Each exec filter and snapshot compressor a fill runs inherited the
slot's lock descriptor beside the stdout it writes into. An flock lasts
until its last copy closes and nothing waits for a process a filter
leaves behind, so a fill killed before its rename could leave the slot
locked, and served stale or uncached, for as long as such a process
lived.

The scan holds its lock across no exec and opens the same way so that
the two stay alike.

0 files changed, 0 insertions, 0 deletions