twistd should write a pidfile on win32

[Jean-Paul Calderone]

Currently _twistd_unix.py takes responsibility for checking and writing pidfiles. This means Windows doesn't do anything with pidfiles at all. At the very least, we can write one.

[zooko]

Here is a related ticket on the allmydata.org "tahoe" trac:

​http://allmydata.org/trac/tahoe/ticket/27 -- "twistd doesn't daemonize on windows"

We currently have a work-around in place for our win32 product, but there are also a few technical details in that ticket that may be interesting.

[zooko]

I guess this is related to #102 -- "Support running Twisted code as NT services on Win32." -- and perhaps to [6678] and [17973].

[Trent.Nelson]

Personally I think effort should be put into running twisted as a service on Windows, rather than replicating Unix type functionality. There really shouldn't be any need on win32 for twistd.pid if using a well written service.

[zooko]

David-Sarah thinks, just because there's been no activity on this ticket in the last five years, that this means Twisted hackers are not going to fix this. What a thing to think! ​https://tahoe-lafs.org/trac/tahoe-lafs/ticket/27#comment:23