- fixed display of dashed helpline, when rotating multiple objects or

around the 3d cursor.
  fix only works for OSX and certain nvidia cards. they need a glFinish()
  call after drawing in frontbuffer.

source/blender/src/drawobject.c

@@ -272,7 +272,7 @@ void helpline(float *vec)
 	setlinestyle(0);
 	
 	persp(1);
-
+	glFinish(); // flush display for frontbuffer
 	glDrawBuffer(GL_BACK);
 }