db_xml.py: put_table(): Don't pass limit, start recursively, because the table subsetting will happen only once in the first invocation of the function. Moved limit, start params to end since they are not passed recursively. start param no longer defaults to 0 because this is not needed since sql.put_table() now sets start to 0 where needed.

sql.py: put_table(): Removed limit and start params because they were never fully implemented, and because it's simpler to just have the caller subset their input table

lists.py: Added uniqify()

sql.py: Moved mk_flatten_mapping(), flatten() to Basic queries section since they don't involve database structure info

sql.py: put_table(): Use single quotes rather than double quotes around strings where possible

schemas/functions.sql, vegbien.sql: Changed CAST-related relational functions to return NULL on data exceptions and convert the exceptions to warnings. This helps column-based import by mapping invalid values to NULL instead of aborting the whole query on the first invalid value.

sql.py: index_col(): Cache the query so it doesn't try to add an index on the same column multiple times

sql.py mk_select(), sql_gen.py Join.to_str(): Fixed bug where conditions needed to be wrapped in () before being AND-ed together to ensure the proper operator precedence

sql.py: put_table(): Add index on columns with invalid values to enable fast filtering

sql.py: Added index_col()