http://forums.urbanterror.net/index.php/topic,13907.0.html
when editing brushes mitre corners.
Mitres can be created using radiant's edge editing tool (press 'e' to enable) or clipping tool (press 'x' to enable).
edge tool:
take a corner and draw it to 45 dregrees
clipping:
make the first clicks to select the cutting line, the third one is for making cuts wit a different angle (i.e. NOT 90 dregrees)
imagine the path of the two points an arrow, 1 is foot, direction goes to two, always the left side will be cut.
xx cut & deleted
1-------------------------2 --->
xx stuff here stays
most general rule:
do not let brushes overlap each other!