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

sql.py: Added cast()

sql_gen.py: Added wrap() and use it in wrap_in_func()

sql.py: put_table(): Track the input column(s) a column is derived from, so that error messages can be attributes to the proper input column(s)