fix translation of trader 'inventory' button
fix up faction-based mounted NPC dismount code -- there is now no way
for a player to issue a dismount command to a faction based NPC (use the
non-mounted variety if you want a non-mounted npc).
faction based mounted units will now kill their horse when they are
repacked into item form (as they will spawn a new horse when respawned)
add bonus armor for equipping a shield in NPC offhand.  
add bonus damage for equipping a weapon in NPC offhand.