db_xml.py: put_table(): Track in_table's source so its original schema can be obtained and auxiliary tables located

sql_gen.py: Derived.set_srcs(): Added optional overwrite param so that a default srcs value can be set only if one isn't already set

sql_gen.py: Made Table a Derived element so that a row-subset temp table could retain the schema of the table it came from, and any auxiliary tables in that schema could be located properly

sql_gen.py: Moved srcs-related functionality from Col to new superclass Derived

sql.py: cast(): save_errors: Fixed bug where srcs needed to have their names extracted before being wrapped in sql_gen.Literals. Fixed bug where errors table INSERT needed to prefix the CROSS JOIN-ed VALUES statements with SELECT * FROM because the CROSS JOIN makes it a whole SELECT query, not just a VALUES statement.

schemas/vegbien.ERD.mwb: Adjusted lines to make less intersections happen on the first page

sql.py: put_table(): MissingCastException: Fixed bug where errors_table needed to have the same schema as in_tables0 as well as part of the same name

sql_gen.py: Added suffixed_table()

sql.py: MissingCastException: Print log message that it's casting the column, to introduce the SQL function definition that follows

sql.py: put_table(): MissingCastException: Use new cast() instead of relying on existing cast functions in the database