pgsql: Fix infinite sleep and failes of send in Win32.

Log Message:
-----------
Fix infinite sleep and failes of send in Win32.

1) pgwin32_waitforsinglesocket(): WaitForMultipleObjectsEx now called with
finite timeout (100ms) in case of FP_WRITE and UDP socket. If timeout occurs
then pgwin32_waitforsinglesocket() tries to write empty packet goes to
WaitForMultipleObjectsEx again.

2) pgwin32_send(): add loop around WSASend and pgwin32_waitforsinglesocket().
The reason is: for overlapped socket, 'ok' result from
pgwin32_waitforsinglesocket() isn't guarantee that socket is still free,
it can become busy again and following WSASend call will fail with
WSAEWOULDBLOCK error.

See http://archives.postgresql.org/pgsql-hackers/2006-10/msg00561.php

Modified Files:
--------------
pgsql/src/backend/port/win32:
socket.c (r1.13 -> r1.14)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/port/win32/socket.c.diff?r1=1.13&r2=1.14)