Bugfix, adjustments

-Fix for guns firing all ammo at once in certain circumstances. Ty
Sestze
-Moved 13L v12 and 5.2L v6 from special to v12 and v6 category,
respectively.  Dupes are unaffected
-75mm AL weight lowered from 2420 to 2125
Added i5 and v10 engines

-Added i5 and v10 engines, and a v10 special. Thanks to Beckett for the
models.
-Buffed 7.0 v12
Merge remote-tracking branch 'upstream/master'