7-button mice (dual wheel) and emacs => segfault

[David Monniaux]

In GNU Emacs 20.5.1 (i386-redhat-linux-gnu, X toolkit)
 of Tue Feb 22 2000 on porky.devel.redhat.com
configured using `configure  --prefix=/usr --libexecdir=/usr/lib
--sharedstatedir=/var --with-gcc --with-pop --with-x-toolkit
i386-redhat-linux-gnu'

Running XFree86 4.0.1 on Linux, I wanted to use the second wheel on my
mouse and bind it to mouse buttons 6 and 7 (the first wheel being bound to
buttons 4 and 5). xev shows button events correctly.

In emacs, moving the second wheel (thus pressing virtual buttons 6 and
7) make emacs get immediately a segmentation fault and core dump.

I know that the X protocol was not supposed to support more than 5
buttons. Nevertheless, emacs should not segfault!

Perhaps adding support for mice with many buttons would be nice: the
second wheel could be used to scroll the buffer
horizontally. Currently, it's possible to make the first one scroll it
vertically.