Add --quote-reserved option to yamltodb.

 * docs/yamltodb.rst: Document new option.
 * pyrseas/database.py (Database.diff_map): Change schemas argument to
   opts and call fetch_reserved_words.
 * pyrseas/dbobject/__init__.py (fetch_reserved_words): New function
   to fetch reserved words from PG.  (quote_id): Use RESERVED_WORDS
   list.
 * pyrseas/testutils.py (InputMapToSqlTestCase.to_sql): Add schemas
   and quote_reserved arguments and pass them to diff_map.
 * pyrseas/yamltodb.py: Add quote_reserved option and pass args to
   diff_map.
 * tests/dbobject/test_table.py: Test for new option.