If no drag can be started on mouse down, don't pick up objects on the way.
Add a preference option to enable Alt+MMB to move the mouse forward and backward.
Fix more precision problems with vertex correction and snapping.
Quickly detect duplicate planes when adding them to a brush.

Signed-off-by: Kristian Duske <kristian.duske@gmail.com>
Merge branch 'refs/heads/Release_1.0.0'

Signed-off-by: Kristian Duske <kristian.duske@gmail.com>

Conflicts:
	Mac/TrenchBroom/TrenchBroom-Info.plist
	Windows/TrenchBroom/BuildNo