- [feature] Added new support for remote "schemas":

  - [feature] Added new support for remote "schemas":
    - MetaData() accepts "schema" and "quote_schema"
      arguments, which will be applied to the same-named
      arguments of a Table
      or Sequence which leaves these at their default
      of ``None``.
    - Sequence accepts "quote_schema" argument
    - tometadata() for Table will use the "schema"
      of the incoming MetaData for the new Table
      if the schema argument is explicitly "None"
    - Added CreateSchema and DropSchema DDL
      constructs - these accept just the string
      name of a schema and a "quote" flag.
    - When using default "schema" with MetaData,
      ForeignKey will also assume the "default" schema
      when locating remote table.  This allows the "schema"
      argument on MetaData to be applied to any
      set of Table objects that otherwise don't have
      a "schema".
    - a "has_schema" method has been implemented
      on dialect, but only works on Postgresql so far.
    Courtesy Manlio Perillo, [ticket:1679]