1. Fix sharp tail detection in normal support.
The not operator in front of overlaps was missing.
2. Fix bridge removal.
After adopting Prusa's smart bridge direction detection, the bridge
angle may be pi, so our previous method (comparing angle to 0 and pi/2)
was not right. Now we simply check if the bridge direction normal vector
is aligned to x-axis or y-axis.
Change-Id: I4e1fd937e432aca97cdd374ba66a0d869794126e
(cherry picked from commit c0d82003a5e4c44345219294072c54051fc5711a)
6facd65530