artwork update: mystic sword

updates the artwork for mystic sword. Its a mashup of the current sword
and the grip of the nerudite sword. 

Currently there is no different between the normal longsword and the mystic sword.

![mystswd_frame2](https://f.cloud.github.com/assets/3530788/175046/8f047b9c-7b36-11e2-86ce-488974839de9.jpg)