Vehicle part duplication bug

Installing a part to a vehicle from around the player (not on them), then installing the same part again (even though it was used) results in a duplication. The crafting_inv cache was not being updated when the player completed installation, even though it checks if the turn was updated (maybe an issue in that?). 

For now, however, this fixes the issue.

-Davek

(P.S. Hey @KA101, I learned about *rebase*. What a neat little feature, heh.)