trouble with use of .cmd() because of selection cleared on blur

[michel2bec]

Great fork of mathquill, really improved.

Now my little problem :

if I add a button to issue : MathQuill.MathField($('#zoneEditable')[0]).cmd('\sqrt')
on a mathquill field with some selected text, it won't work as expected (put a square root around the selected text) because clicking the button causes blur() on the mathquill field which does cursor.clearSelection(); in Controller.focusBlurEvents (in blurTimeout).

This makes the cmd interface a lot less usefull.

(for my personnal use case I just commented out cursor.clearSelection(); : as I don't really know what was initially intended with this cursor.clearSelection(); action, I won't submit a patch)