Added IPC Strand and Coordinator classes. Strands are jobs responsible

Added IPC Strand and Coordinator classes. Strands are jobs responsible
for registering Squid processes or threads with the central Coordinator
job. Coordinator will broadcast control signals and shared ports to
Strands.

Added a simple hierarchy of inter-process communication (IPC) classes to
support Coordinator and Strands.

Print current process number (KidIdentifier) when writing debug messages.
This allows to easily isolate per-process progress even when using a single
cache.log.