Wrap close(), use closesocket() on WIN32/WinSock.

The server_socket library (used by the httpd output plugin) didn't
check for WIN32, that's fixed now.

Allocate a player_control object where needed, and pass it around.
Each "client" object is associated with a "player_control" instance.

This prepares multi-player support.

This is portable for win32 and fixes client logins there.

After we've been hit by Large File Support problems several times in
the past week (which only occur on 32 bit platforms, which I don't
have), this is yet another attempt to fix the issue.

The soure file client.c has nearly 1000 lines, time for splitting it
into smaller pieces to improve readability.