sql_gen.py: Use an as_*() function instead of manually checking the type wherever possible

sql.py: mk_insert_select(): INSERT IGNORE: Added duplicate key handling by using EXCEPTION block to catch unique_violation

sql.py: mk_insert_select(): INSERT IGNORE: Fixed bug where user-defined types were not supported correctly, by referencing the column's type directly in PL/pgSQL instead of retrieving it from the information_schema. Use a row variable of the output table's row type to store the select query data, so that you don't need to create a separate local var for each output column.

import.stats.xls: Changed \/row (ms)" to "ms/row"

sql.py: mk_insert_select(): INSERT IGNORE: Used typed vars to store each column of the select query because the select query's column names are not known, so it would be unknown which record var column to use for each output column. (Add types so there are no unknown-type values that PostgreSQL will say can't be cast.)

sql.py: insert_select(): In ignore mode, always recover from errors

sql.py: mk_insert_select(): INSERT IGNORE: Implemented simple cursor loop that just inserts each row, without ignoring duplicate keys

sql.py: mk_insert_select(): Added ignore param to do an INSERT IGNORE equivalent operation. Added basic structure for INSERT IGNORE. Support embeddable queries without RETURNING columns (which is the case for most INSERT IGNORE queries).

sql.py: run_query_into(): Always set into.schema to None, so that table is created in the temp schema in debug_temp mode

sql.py: DbConn.DbCursor.execute(): Don't cache ADD COLUMN queries because the rest of the query must be unique in order to use caching