Staging: pohmelfs: transaction layer.

This patch implements transaction processing helpers
used to allocate/free/insert/remove and other operations
with the transctions.

Each transction is an object, which may embed multiple commands
completed atomically. When server fails the whole transaction will be
replied against it (or different server) later. This approach allows to
maintain high data integrity and do not desynchronize filesystem state
in case of network or server failures.

Signed-off-by: Evgeniy Polyakov <zbr@ioremap.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>