Currently wonders have 300 <Loot/xp>, centres 200, defensive structures 100, other structures 0. However, a short palisade segment (200 health) is much easier to destroy than an iber fortress (6000 health) or cart wall tower (12000 health), therefore it does not really make much sense they all give the same amount of experience.
This patch sets <Loot/xp> to 10% of <Health/Max> for structures that have <Attack> (i.e. are capable of shooting projectiles), and 0 for others (including Wonder).
(Also cleaned up a few lines.)