sql.py: with_parsed_errors(): Raise DuplicateTableException for "relation already exists" errors instead of "table name specified more than once" errors

sql.py: run_query_into(): Removed "DROP TABLE IF EXISTS" because sometimes when there are collisions in the temp table names, the code actually uses both "copies" of the temp table. Eventually, this situation will be resolved by adding a counter to the temp table name.

sql.py: Cleaned up DbException's and subclasses' messages

exc.py: ExceptionWithCause: Added cause_newline option to put the cause on its own line instead of on the message line

sql.py: with_parsed_errors(): Also parse "table name specified more than once" errors as DuplicateTableExceptions

sql.py: put_table(): Handle DuplicateKeyExceptions by running a select query on the unique constraint columns

sql.py: mk_select(): Support tuples of tables, not just lists

sql.py: with_parsed_errors(): Support table names that start with "_"

sql.py: DbConn: Added with_savepoint(). with_savepoint(): Use new DbConn.with_savepoint().

schemas/functions.sql: Added _toBool