Selecting windows with the mouse.

[dlw at MIT-AI (Daniel L. Weinreb)]

When you single-click-left on a non-selected editor window, the point
gets moved to where you click.  This means that rather than just having
selected the window, you have also changed its state, by messing up the
position of point.  If you want to just plain select it, and want the
position of point to stay the same (because it is somewhere useful), you
have to double-click, and that warps the mouse.

I don't think this is the right behavior (although I am not completely
sure); it seems that there should be an easy way to simply select the
window so that keyboard input goes to it, by pointing to it, and that
since the way I always do that with any other program is with
single-click-left, it ought to be that way for the editor too.