#1 Middle button should zoom

[Stuart Axon]

Most modern mice will let you press the wheel - this is more convenient for zooming than pressing both buttons at the same time.

Possibly rolling the wheel should also zoom in and out.

[Mikael Hvidtfeldt Christensen]

You are right about that - it used to work, but I must have broken it at some point.
(Since I do not have a scroll wheel on my laptop, it is not easy to detect :-))

But I've corrected the error, and it will work again in the next release.