Fixed a bug where starting tilting with LMB+RMB with LMB in sketcher
caused odd behavior.
No more messagebox upon hitting H key when the cursor is over nothing
(replaced with a warning). The messagebox was very annoying when trying
to hunt a point with touch input.
Navigation by gestures didn't work after double-clicking a constraint in
sketcher to edit a value. This was probably caused by the last mouse
button release event not reaching the viewer.
