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

maximusmai/sqlalchemy-migrate,AlanZatarain/sqlalchemy-migrate,aishee/sqlalchemy-migrate,Alwnikrotikz/sqlalchemy-migrate