fix generation of foreign key constraint name in migrate.changeset.constraint.ForeignKeyConstraint.autoname
fix generation of foreign key constraint name in
migrate.changeset.constraint.ForeignKeyConstraint.autoname

use <table>_<firstcol>_fkey instead of <table>_<reftable>_fkey

Fixes Issue 101
dannon/sqlalchemy-migrate,openstack/sqlalchemy-migrate,openstack/sqlalchemy-migrate,rcherrueau/sqlalchemy-migrate,andras-tim/sqlalchemy-migrate,emontyoncrack/wookie18,stackforge/sqlalchemy-migrate,emonty/sqlalchemy-migrate,rcherrueau/sqlalchemy-migrate