Fix: fix fixed weapon

Sometimes I want strange things: droid-medic, PSI-tank. But OpenXcom wants to move all of them into backpack. This commit does simple thing: fixed weapons always placed into "hands".
![screen007](https://cloud.githubusercontent.com/assets/3616568/4350227/b69f2552-41dd-11e4-93f5-3ed4efe902f1.png)