unixctl: Add support for Windows.

unixctl: Add support for Windows.

For Windows, use a kernel assigned localhost TCP port to listen for
runtime management connections and then write it into a file
so that a client can read it and then make a TCP connection.

Since we do not have the infrastructure to create pidfiles on
windows as of now, we create the *.ctl file without a pid. This
should be okay since we use different OVS_RUNDIR when we run
multiple copies of a daemon.

We do not generate man pages on Windows. But we still update them
for Windows so that anyone can read it elsewhere. Since we do not
generate it directly, we cannot dynamically show the configured
OVS_RUNDIR in windows. So, I have a not so nice \fIOVS_RUNDIR\fR
in the man page.

Signed-off-by: Gurucharan Shetty <gshetty@nicira.com>
Acked-by: Ben Pfaff <blp@nicira.com>