MYSQL ONLY: store table_schema, specify in queries, make DB(schemas=) work.

NOTE: BREAKS ALL NON-MYSQL. Changed mysql.py to specify schema in table
queries, fixing a bug where two tables with the same name in different
schemas cause errors when one schema is excluded. Also fix small issues
in the code where schemas are first specified, allowing it to actually
work.
Merge remote-tracking branch 'origin/master'

Conflicts:
	db/db.py