Fix egs_circle_perpendicular critical bug

[rtownson]

Fix a bug in egs_circle_perpendicular that made the geometry invalid for any cases where the circle was expected to face away from the z-axis. Anyone who used this geometry should check their results.

This bug persisted because testing was done on a version where a similar fix had been done, but never included in the distribution.

Example that incorrectly produced a line target instead of a circle:

   :start source:
     library = egs_collimated_source
     name = isotropic_collimated_source
     :start source shape:
       type = point
       position =  900 0.000000 0.000000
     :stop source shape:
     :start target shape:
       library = egs_circle_perpendicular
       midpoint = 0 0
       radius = 25
     :stop target shape:
     charge = 0
     :start spectrum:
      type = monoenergetic
      energy = 2
     :stop spectrum:
   :stop source: