CREATE INDEX on ForeignKey crashes during table creation
Fix https://github.com/coleifer/peewee/pull/304

When doing MyModel.create_table(), MyModel containing a ForeignKeyField, the creation of the related index doesn't work, because it complains that the relation is missing (MyModel's table)

I've also notices that the CREATE INDEX sql misses the table schema. I've tried fixing it at line https://github.com/coleifer/peewee/blob/master/peewee.py#L1321 :

tbl_name = ('.').join([model_class._meta.schema,model_class._meta.db_table])

but this doesn't solve the problem. Maybe the table hasn't been created yet when the create index is issued? Am I doing something wrong?
