Remove need to use "set search_path" in various commands. Fixes #73.

 * docs/dbobject.rst: Remove DbSchemaObject.set_search_path.
 * pyrseas/dbobject/__init__.py (DbSchemaObject.qualname): Add objname
   argument to allow qualification of related objects.
   (DbSchemaObject.set_search_path): Delete.
 * pyrseas/dbobject/column.py (Column.set_sequence_default): Don't set
   search_path but qualify table name instead.
 * pyrseas/dbobject/index.py (Index.create): Don't set search_path but
   qualify table name instead.
 * pyrseas/dbobject/table.py (Sequence.add_owner): Don't set
   search_path but qualify sequence and owner table instead.
 * tests/dbobject/test_column.py: Modify
   test_create_table_with_defaults to use a non-public schema and to
   verify ALTER SEQUENCE OWNED BY.
 * tests/dbobject/test_index.py: Add new test to verify index creation
   in a non-public schema.