Fix for issue #114
Changed ForceJump to explicitly set groundEntityNum to ENTITYNUM_NONE.

On high server's framerate the code for detecting NPC jumps can be run multiple times before the NPC's think function is executed.
So the NPC does not get time to detect that it has left the ground before it would again check for a jump, resulting in incorrect velocity for the jump.
Merge pull request #194 from xScooper/master

Fix for issue #114