backups/Makefile: Full DB: Added vegbien.backup/all to run both test and rotate

README.TXT: Renamed Maintenance section to Backups for clarity

backups/Makefile: .sql: When testing, turn it off so make won't skip `.sql: %` in favor of it

backups/Makefile: Split %.backup and %.sql into separate targets for clarity

inputs/import.stats.xls: Updated with stats from latest import. Note that this import adds data provider feedback for SQL functions as well as additional date processing using _date().

schemas/py_functions.sql: _date(): Re-enabled now that exceptions thrown are properly handled. FormatException: Support raising parsable data_exceptions when provided with the value that was invalid. Date parsing mode: Return date as the value in FormatException so it can be filtered out automatically by column-based import.

sql_io.py: put_table(): is_function: Creating error handling wrapper function: Fixed bug where needed to cast NULL returned in error handler to appropriate type, because it's contained within a SELECT query which does not do implicit casts from type unknown

sql_gen.py: Cast: Support types which are Code objects

sql_io.py: func_wrapper_exception_handler(): Use new sql_gen.merge_not_null() to try to ensure that NULL values are not folded (which would cause the concatenated values not to match up with the concatenated column names). Note that this adds a dependency on the db object, which callers must now provide.

sql_gen.py: Added merge_not_null()