schemas/vegbien.sql: Made datasource_id required on every table that has it, to trigger the automatic population of it by sql_io.put_table()'s col_defaults

Moved importing of col_defaults from db_xml.put_table() to bin/map, so that it also happens in row-based mode. Note that this causes a DB entry for the datasource to always be created, even if the datasource has no mappings or no rows.

Use new exc.reraise() where exc.raise_() was used, so that the stack trace is preserved when the exception is rethrown

exc.py: reraise(): Take optional exception argument so it can be invoked in the same way as raise_(). Interestingly, this missing parameter does not produce the usual "...() takes no arguments (1 given)" error when the function is called inside an except block.

exc.py: Added reraise()

db_xml.py: put(): Inserting node: Wrap sql_io.put_table() call in catch-all exception handler that calls on_error_() (wrapper for error handler provided by caller) and returns None. This both adds additional debugging info to the exception (in on_error_()) and allows recovery from arbitrary exceptions that happen in sql_io.put_table(), so that an exception does not abort the import.

exc.py: get_e_tracebacks_str(): Use the current system traceback if the exception doesn't contain its own traceback(s)

schemas/vegbien.sql: specimenreplicate: Added locationevent fkey, since fkeys are not inherited from parent tables

schemas/vegbien.sql: Added datasource_id fkey constraints to all tables that needed it

bin/map: out_is_db: Use col_defaults in row-based mode as well