Fix for bug #527:

https://github.com/warpech/jquery-handsontable/issues/527

This is a version of the fix in:

https://github.com/psmolenski/jquery-handsontable/commit/983e13a2cb27ece41127e6b76c23be83dac9a53d

... but back-ported to the 0.9.11 branch, basically, because when I
tried to upgrade to 0.9.12 to get this bugfix, it broke column moving in
a different way that I couldn't debug.