win32 service code

Hi!

Last I spoke with Claudio, he was still waiting for some reactions from
others than me on how we want the service code. So I figured I'd post a
recap of the options we have. I've added some advantages/disadvantages,
but those are my thoughts only. There are sure to be others.

1) Separate binary "pgservice.exe" that will CreateProcess() the
postmaster.exe.
Advantages: Zero impact on postmaster code. Simple to do.
Disadvantages: Adds a platform-specific binary.

2) Include in postmaster doing an extra CreateProcess().
Advantages: No extra binary. Low impact on postmaster code.
Disadvantages: Two postmaster.exe:s. running (confusing? overhead?)

3) Include in postmaster but running on a separate thread (not process
as (2))
Advantages: No extra binary. No extra process. Most integration.
Disadvantages: Probably larger impact on postmaster code.

As said, I've probably missed some in adv/disadv, but I think I got all
our options.

Thoughts?

//Magnus