new_contents: # coding=utf-8
  """fix models db differences
  
  Revision ID: 491607abf93d
  Revises: 2793805922ab
  Create Date: 2015-04-27 13:19:30.567000
  
  """
  
  # revision identifiers, used by Alembic.
  revision = '491607abf93d'
  down_revision = '2793805922ab'
  
  import datetime
  
  from alembic import op
  import sqlalchemy as sa
  
  
  def upgrade():
      op.drop_table('unitparameterunit')
      op.drop_table('unitparameterunit_history')
  
      with op.batch_alter_table('ref_history') as b:
          b.add_column(sa.Column('language_note', sa.Unicode))
          b.add_column(sa.Column('ca_language_trigger', sa.Unicode))
          b.add_column(sa.Column('ca_doctype_trigger', sa.Unicode))
  
  
  def downgrade():
      pass
  
subject: add missing ref_history cols, drop orphaned tables