[z2402] Revert "[z1818] make armor bonuses from certain items be unaffected by base armor mods"

Thanks to @Velvet
Fix Rockbiter Weapon and remove some TBC-specific code.

Also clean-up SPELL_EFFECT_ENCHANT_ITEM_TEMPORARY and fix some enchantment
durations.
Merge pull request #49 from Patman64/rockbiter

Fix Rockbiter Weapon and remove some TBC-specific code.