A go at trying to remove the performance regression in hash primary key access.

Inline tuple_field_old(), which avoids a function call
for field 0 access.
A hack to fix opentar-42 (mail.ru ticket).

What happened in production, during upgrade:
- logger option in the config file was pointing to nowhere
- the server would start, unable to check that the child logger
process died prematurely
- the server would fork spawner process to spawn replication relays
- a replica would come in, asking for data
- the spawner would successfully spawn a relay but die on SIGPIPE
when trying to write to the log (a pipe leading nowhere by now)
about the event
-> we have a master with a dead spawner process, no more replicas,
sorry.

Well, someone should check their configuraiton in the first place.
Nevertheless, try to be nice, and:

- don't die on SIGPIPE in the spawner process.
- when starting the logger, make an effort to check that it has started
successfully. There is no reliable way to find this out, so do
it with the best effort.
Merge branch 'stable'