Intro
=====
I run KDE and I have it set to use a left handed mouse.  xev for example
understands the swapped buttons.  However, when I run any gtk+ 3 app,
there are weird focus issues with the mouse.  It's not that gtk+ simply
treats button 1 and 3 the wrong way round, as the following example
shows.

Steps to reproduce
===================
1. Run a left handed KDE session.
2. Run gtk+/tests/testbuttons
3. Mouse down on any GtkButton ("GtkButton 1") with mouse button 1,
   i.e. index finger of left hand.
4. Mouse up with pointer either over the same GtkButton or not
5. Mouse down with mouse button 1 on "GtkButton 2", which shall be any
   GtkButton other than "GtkButton 1"

Expected results
================
The "GtkButton 2" is depressed.

Actual results
==============
The "GtkButton 1" is depressed, as if it has grabbed the focus.

Other
=====
These issues disappear if I switch the KDE mouse setting to right
handed.

It's not entirely clear to me that this is a gtk+ bug and not a KDE bug.
However, I don't encounter the issue in gtk+ 2 apps.  In particular,
only from gtk+ commit c4a5c2ed4b8861f92104f51d9213b0c9f64e26b1 ("Enable
XI2 by default") do I encounter the problem.