win32 signals, part 4

Ok, here we go again.

Taking into account Claudios comments on the previous patch, as well as
some more fooling around here of my own, here's a fourth (and final?)
one.

If there are no further comments from Claudio or anyone else, I feel
this is now ready to be applied.

Differences from last version:
1) Per Claudios suggestion, create a "babysitter thread" for each
process that waits on the process and signals ourselves. This reduces
the amount of code (=good) and most importantly removes all the
synchronisation issues (=even better). The only thing left to sync is
the signal delivery, and that has alreay been taken care of in previous
patches.

2) Make pg_queue_signal() no longer be static. This way we don't have to
go through named pipes when signalling ourselves.

3) Remove the redefinition of select() again. This also means that the
select.c file previously incouded should *NOT* be included any more. See
separate mail to hackers-win32 on this issue.

4) Fix Claudios wrong-assignment error in win32_removeChild. Also
improve an error message in win32_waitpid.

Again, the preivously attached select.c file should *NOT* be included.

//Magnus