As reported by J0k3r613, patched guild system not recognizing properly
the guild leader just after creation. Patched many more issues related
to guilds and alliances.
Implemented Guild PQ. Fixed a problem introduced earlier where negative
EXP would be deemed as "integer overflow", provoking many game breaking
issues as result.
Added mechanics for the EXP/DROP cash coupons (such as enabling
out-of-time active coupons via command and automatic update of active
ones over the designed interval). Created MapleCouponInstaller as means
to gather info about the coupon intervals and rates from the WZs (the
generated SQL table is already updated on the db_database.sql file).
