xfree86: fix wrong DontZap documentation (#71113)

X.Org Bug 71113 <http://bugs.freedesktop.org/show_bug.cgi?id=71113>

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
(cherry picked from commit e48a132b6d187f355abd7021be47edde972e7091)
man: drop specific mention of DontZap in -retro (#71113)

DontZap off is the default anyway, don't mention it specifically to avoid
confusion

X.Org Bug 71113 <http://bugs.freedesktop.org/show_bug.cgi?id=71113>

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
(cherry picked from commit cfaf2abbac3f01e57d00845d8908bf01559263f9)
Fix overflow checking extension versions

The easiest way to check for the version of an extension is to send the maximum
possible version numbers in the QueryVersion request. The X server overflows on
these as it assumes you will send a reasonable version number.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Keith Packard <keithp@keithp.com>
(cherry picked from commit 548fc937b22d4dfe7f96e0bd77522261603a2c2f)
Xi: block SIGIOs while copying device classes around

I've been seeing sporadic (anywhere from once every few days to 3-4
times a day) crashes and freezes in X. The problematic behaviour isn't
always the same, but I chose a particular incident to debug, and found
that X was segfaulting in updateMotionHistory, on line 575 of
dix/getevents.c.

After some further investigation, I found that the bug was being
triggered when a SIGIO was received in DeepCopyPointerClasses, between
the AllocValuatorClass call (line 540) and updating the to->valuator
pointer (line 545). AllocValuatorClass calls realloc() on to->valuator,
so between these lines, it's not guaranteed to point to allocated
memory.

It seems the SIGIO handler is calling updateMotionHistory, which is
reading the memory pointed to by to->valuator and getting a wrong value
for last_motion, which updates buff to point to wildly the wrong place
and thus generates a segfault when a memcpy() is done into buff.

I am attaching a patch which I've been running on that machine for the
past three days, and haven't yet observed any more crashing or freezing
behaviour. The patch simply calls OsBlockSIGIO while
DeepCopyDeviceClasses is in progress, as the state of the X server's
device data structures is not guaranteed to be in a consistent state
during that time.

Debian bug#744303 <https://bugs.debian.org/744303>

Signed-off-by: Julien Cristau <jcristau@debian.org>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
(cherry picked from commit d7a2df0a7499864cb005b098b79c1bdf884f6600)
Bump version to 1.15.2

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>