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

Unfortunately, there's no "optimized" implementation here.  We can't
use Linux's proprietary system call dup3(), because it would require
us to specify the new descriptor.

This function is empty on WIN32, but we need to return a value.

Use the correct parameter name.

This fixes an assertion failure.

All sources which might work with large files must include config.h,
to get Large File Support on 32 bit platforms.

Add a "mode" argument to open_cloexec() instead.

Same as pipe_cloexec_nonblock(), but doesn't set non-blocking mode.

We'll copy this code to libmpdclient, and that's easier if its license
is BSD.

Changed the wrappers for pipe(), socket(), accept().  On WIN32, this
does not work for pipe().

This function is used only internally.

Added wrapper for inotify_init1() to fd_util.c.

Added the "fd_util" library, which attempts to use the new thread-safe
Linux system calls pipe2(), accept4() and the options O_CLOEXEC,
SOCK_CLOEXEC.  Without these, it falls back to FD_CLOEXEC, which is
not thread safe.

This is particularly important for the "pipe" output plugin (and
others, such as JACK/PulseAudio), because we were heavily leaking file
descriptors to child processes.