g_io_channel_win32_new_fd() and is_*able

[Ron Steinke <rsteinke w-link net>]

Hans,
	Looking at you implementation of g_io_channel_win32_new_fd(),
you use fstat() to determine whether to set is_readable and is_writeable.
Under UNIX, fstat() just returns file permissions, and you need to
use fcntl() to determine whether the file was opened for reading,
writing, or both. Is the same true for win32?

Ron Steinke