require only one of the two entities to target the other for warpzones, instead of...

require only one of the two entities to target the other for warpzones, instead of a cyclic connection

Now, warpzone layout is:

trigger_warpzone --killtarget--> target_position for origin and direction
                 --target------> trigger_warpzone --kiltarget--> target_position for origin and direction

         ^
         |
+--------X--------+
|         _       |
+--------|\-------+
           \
            \
             \  ^
              \ |
        +------\X--------+
        |       \        |
        +----------------+

git-svn-id: svn://svn.icculus.org/nexuiz/trunk@8686 f962a42d-fe04-0410-a3ab-8c8b0445ebaa