Miter Cut in 2.5 Beta

I am creating trim around a door.
How do I miter the corner to get an accurate 45 degree cut?
Is there a way to intersect the extrusion with the 45 degree plane I created?


In 2.49, use the Knife (exact), and Ctl-click to snap the cut line to the ends of the 45 degree plane.
In 2.53, snapping the knife cut to vertices is not implemented yet :(.

Best wishes,

I use shear tool.
In edit mode select the top vertex
Search: shear
Middle mouse to change orientation and type 1 or -1 to a perfect 90º angle.