include: add close_fd() for noticing write errors before close()

include: add close_fd() for noticing write errors before close()

Essentially this helper function is similar to close_stream(), but for
file descriptors.

When a file descriptors are close()'d status of write is often
overlooked.  The close_fd() will try to determine what happen to writes
with fsync() before closing the file descriptor.

Signed-off-by: Sami Kerola <kerolasa@iki.fi>