debian bug 1034054: backport fvwm3 xthreadlock()

[ThomasAdam]

Backport this fix from fvwm3 to fvwm2:

fvwmorg/fvwm3@5c17c83

[hills]

I've been running this patch for nearly 1 week now and it has fixed the related crashes, so I recommend it for merge into the 2.x series as a priority. An update to libX11 means a regression in FVWM behaviour and this patch prevents it.

[somiaj]

There is a minor issue with this patch, that although fvwm no longer crashes (woot), some expose events are lost and icons do not refresh correctly. See fvwmorg/fvwm3#818, which hasn't been fully resolved, though there is some ideas of how to fix that issue.

Note the icon issue is much smaller than the crashing issue, so probably best to at least not crash. This patch is included in Debian's package, though fvwm is basically not supported, so it even if this gets merged, a new release might not be made. In either case users should grab this patch to avoid the libx11 change.