bug#11825: 24.1.50; float-time no longer accepts negative time values

[Paul Eggert]

On 07/07/2012 07:57 PM, Eli Zaretskii wrote:
> are you saying that a time difference can
> never be negative on such platforms?

Yes, that's right.

> What about the case tv_sec = 0
> in both time values and tv_nsec difference is negative?

In that case, timespec_sub returns the
minimum possible time value, namely zero,
since time_t is unsigned.

> There's nothing wrong with sys_select on msdos.c

Yes, the code works now, I'm just trying to simplify
Emacs by removing the need for EMACS_TIME_SIGN so that
we can remove EMACS_TIME_SIGN.  It's no big deal.