EnchanterRecipes_Core.xml: Add repair enchant (thaumcraft)

Thaumcraft's "repair" enchant can be created consistently using
Infusion Enchantment, with salis mundus and an anvil. The anvil
struck me as more evocative. Level cost is 6/12 for levels 1/2,
so I kept costPerLevel = 6.
Merge pull request #1488 from seebs/master

EnchanterRecipes_Core.xml: Add repair enchant (thaumcraft)