schemas/vegbien.sql: Added cast functions for enum types which map invalid values to NULL

sql.py: put_table(): Fixed bug where some exceptions with no handler would not even allow insertion of no rows into the out_table (due to type mismatch issues), by creating an empty pkeys table as a special case

sql.py: put_table(): Preparing to insert new rows: Fixed bug where main_select needed to be generated after distinct_on was set in the if statement

sql.py: put_table(): log_exc(): Fixed bug where the exception strings rather than the exceptions themselves needed to be put in the set, because exceptions are not comparable with ==

sql.py: put_table(): Moved mk_main_select() call out of try block since it is not related to the exceptions that may be thrown

sql.py: put_table(): log_exc(): Check if exception already caught before to avoid infinite loops

Added debug2redmine and helper file debug2redmine.csv

sql.py, db_xml.py: Removed unnecessary calls to sql_gen.clean_name() now that str() handles this automatically

sql_gen.py: sql_gen classes inherit from new base class BasicObject, whose str() calls clean_name() on the object's repr(). Changed the main debug-repr producing method to be repr() instead of str().

Moved clean_name() from sql.py to sql_gen.py because it's DB-general and so that it can be used by sql_gen.py without circular dependencies