[AD] Patch for retrac_* objects

["Eric Botcazou" <ebotcazou@xxxxxxxxxx>]

This patch changes the behaviour of the 'retrace_count' variable and
'retrace_proc' callback when the retrace simulator is not installed.
Previously, they were incremented and called respectively 70 times a second,
whatever refresh rate was being used. This patch lets them use the refresh
rate if it is known (i.e non zero).

Note that this behaviour has been implemented for the Windows port since the
very beginning, inconsistent with the docs and the other ports.

The motivation behind this patch is for the Windows port to get rid of its
custom timer code and use the high-level _handle_timer_tick() routine from
src/timer.c instead.

Compiled under DJGPP and Mingw32.

--
Eric Botcazou
ebotcazou@xxxxxxxxxx

Attachment: retrace.zip
Description: Zip compressed data