Polished shared memory initialization sequence, using RunnersRegistry API.

Polished shared memory initialization sequence, using RunnersRegistry API.

The master process is now responsible for initializing all shared memory
segments before starting kids. The kids do not create new segments and attach
to the already initialized segments instead. This approach may not scale for
ever, but it avoids more complex initialization synchronization via
Coordinator.

Do not use Strings for globals because current string memory pools do not
support early initialization.