XI2 pull warning

[Thomas Jaeger]

> 
>> * It seems to be pretty easy to crash the server using XI1 applications.
>>  I'll provide more information later
> 
> Yes please. I'd need some sort of test-case to debug crashes.

Here's an easy to reproduce way to crash the server:  Float the virtual
XTest core pointer (you can't do this directly, but either a XI1 or XI2
grab will do), and then issue an XTest pointer event.  The server will
crash with a zero-dereference in Xext/xtest.c, line 386.

Tom