Log Message:
py-alembic: updated to 0.9.8

version: 0.9.8
Fixed bug where the :meth:.Script.as_revision_number method
did not accommodate for the 'heads' identifier, which in turn
caused the :meth:.EnvironmentContext.get_head_revisions
and :meth:.EnvironmentContext.get_revision_argument methods
to be not usable when multiple heads were present.
The :meth:.EnvironmentContext.get_head_revisions method returns
a tuple in all cases as documented.

Fixed bug where autogenerate of :class:.ExcludeConstraint
would render a raw quoted name for a Column that has case-sensitive
characters, which when invoked as an inline member of the Table
would produce a stack trace that the quoted name is not found.
An incoming Column object is now rendered as sa.column('name').

Fixed bug where the indexes would not be included in a
migration that was dropping the owning table.   The fix
now will also emit DROP INDEX for the indexes ahead of time,
but more importantly will include CREATE INDEX in the
downgrade migration.

Fixed the autogenerate of the module prefix
when rendering the text_type parameter of
postgresql.HSTORE, in much the same way that
we do for ARRAY's type and JSON's text_type.

Added support for DROP CONSTRAINT to the MySQL Alembic
dialect to support MariaDB 10.2 which now has real
CHECK constraints.  Note this change does **not**
add autogenerate support, only support for op.drop_constraint()
to work.