[WINDOWSNT]: Include winsock.h and ntlib.h.

[WINDOWSNT]: Include winsock.h and ntlib.h.
Macro SOCKET_ERROR undefined.
Don't declare h_errno.
[!WINDOWSNT]: Define macros recv and send.
[!WINDOWSNT] (POP_SERVICE): Change to pop3.
(pop_open) [WINDOWSNT]: Initialize trash_started.
(have_winsock) [WINDOWSNT]: New variable.
(socket_connection) [WINDOWSNT]: Initialize winsock.
(socket_connection): Use closesocket instead of close.
(getline): Use recv instead of read.
(fullwrite): Use send instead of write.
(pop_trash): Use closesocket instead of close.
(pop_trash) [WINDOWSNT]: Cleanup winsock.
Check if being called recursively by sendline.