input.Makefile: Staging tables installation: Treat any .sql file whose name contains (not just ends with) "schema" as a schema file and sort it before other .sql files

schemas/vegbien.sql: Functions containing UPDATE statements: Use quote_nullable() instead of quote_literal() to properly encode NULL values

schemas/vegbien.sql: Functions containing UPDATE statements: Use PL/pgSQL's EXECUTE statement to avoid caching query plans. This is necessary because as the table grows over time, the optimal query plan may change.

sql_io.py: put_table(): ensure_cond(): When deleting rows rows that do not satisfy the condition, handle sql.DoesNotExistExceptions caused by columns in the condition that were not replaced with NULL. These occur when out_table is a function, and the columns of the table the condition relates to therefore can't be found using out_table.

sql_io.py: put_table(): Calling function: Do not cache the function call, because it may be retried after error handling

sql_gen.py: NotCond: Treat a condition that evaluates to NULL as false instead, so that the boolean effect of the condition is completely inverted

sql_gen.py: null_as_str: Use new null instead of hardcoding 'NULL'

sql_gen.py: Added null

sql.py: run_query(): Give failed EXPLAIN approximately the log_level of its query, so that queries which produce an error in the EXPLAIN before the query itself is even run will still be logged

sql_io.py: put_table(): sql.DatabaseErrors: Factored exception-handling code out into handle_unknown_exc(), for use by other exception handlers