(init_environment): Read PRELOAD_WINSOCK from registry if

(init_environment): Read PRELOAD_WINSOCK from registry if
not set in environment.

(winsock_inuse) [HAVE_SOCKETS]: New variable.
(have_winsock) [HAVE_SOCKETS]: Obsolete variable removed.

(term_winsock) [HAVE_SOCKETS]: Only unload winsock library if there
are no active sockets still open, and if the cleanup function
succeeds.  Return TRUE if winsock is unloaded.

(init_winsock) [HAVE_SOCKETS]: Load winsock if not already loaded,
and return TRUE if winsock support is available.  Unload winsock
immediately if new parameter load_now is false.  Check that
WSAStartup supports the winsock version we requested.

(set_errno, check_errno, sys_socket, sys_bind, sys_connect, sys_htons,
sys_ntohs, sys_inet_addr, sys_gethostname, sys_gethostbyname,
sys_getservbyname, sys_close, sys_read, sys_write) [HAVE_SOCKETS]:
Check winsock_lib instead of have_winsock to determine if winsock
support is available.

(sys_socket, sys_close) [HAVE_SOCKETS]: Count sockets in use.

(init_ntproc) [HAVE_SOCKETS]: Only load winsock library on startup
if PRELOAD_WINSOCK is set in environment (or registry).