Cygwin: winpids: Fix getting process multiple times

Cygwin: winpids: Fix getting process multiple times

Switching to Cywin-only PIDs introduced a new problem when collecting
Cygwin processes for `ps -W': A process can show up multiple times
again, if the Cygwin procinfo has been opened for a just execing
process.  The execed process then shows up twice, once as Cygwin
process, but with the wrong Windows PID of the execing process,
once as Windows-only process.

The mechanism used to exclude these stray processes didn't work with
the new Cygwin pid handling anymore.  To fix this

* check if the incoming Windows PID is the same as the PID in the
  procinfo.  If not, we have the PID of the execing process while
  procinfo was already changed,
* always check if the process has already been handled, not only
  for processes we got a procinfo for,
* simplify adding pid to pidlist since pid is now always correct.

While at it, fix comments and comment formatting.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>