lib/sql.py: distinct_table(): don't cache the table creation, because this prevents different distinct_tables from being created for the same input table

lib/sql.py: create_table(), copy_table_struct(): support custom query options, such as cacheable

lib/sql_io.py: put_table(): main loop MissingCastException handler: factored out into nested function so that it can also be used elsewhere

lib/sql.py: parse_exception(): parse "operator does not exist" errors as MissingCastExceptions (these appear when a staging table column is of the wrong type)

bugfix: /README.TXT: Full database import: Check that source contains [# datasources] rows up through XAL: added alternative verification method when this is not the case (some datasources may be near the end depending on import order)

schemas/vegbien.sql: public_validation: split into separate subschemas for plots, specimens, traits

schemas/Makefile: vegbien.sql: support auxiliary schemas besides *_validation

fix: schemas/Makefile: %/publish: removed no longer applicable instructions about running `make schemas/rotate`. you should not publish a schema until you are satisfied that it can replace the previous public schema, so that the previous public schema doesn't need to be saved.

fix: schemas/vegbien.sql: public_validation comment: undid incorrect replacement of "validation" with "public_validation"

bugfix: schemas/Makefile: "public": dont