Render the default value in the way it correctly reflects the type of the original value.
Render the default value in the way it correctly reflects the type of the original value.

This is needed to deal with the case where the coercing isn't supposed to work, as follows:

mysql> CREATE TABLE foo (t1 TIMESTAMP DEFAULT '0');
ERROR 1067 (42000): Invalid default value for 't1'

ideadevice/alembic,6si/alembic,6si/alembic,moonrabbit/alembic,fsys/alembic,fsys/alembic,ideadevice/alembic,graingert/alembic,chishaku/alembic,zzzeek/alembic,Frozenball/alembic,Frozenball/alembic,moonrabbit/alembic,sqlalchemy/alembic,ImaginationForPeople/alembic