This fixes a file descriptor leak in Windows that happened in the
logging code. The most visible effect of this was if you had a
log::maxsize set then on Windows you would see:
"Max file size reached, starting new log file"
Every other line, forever (and not actually starting a new log).
fd_close() previously did not close the file descriptor of a file
on Windows because on Windows it needs to call close() for a file
and closesocket() for a socket, and it always did the latter.
On *NIX it's more easy and you can just always close() any fd.
Bram Matthys
329f48334c