sql_gen.py: plpythonu_error_handler: Fixed bug where not all PL/Python exceptions start with "PL/Python: " (e.g. on PostgreSQL 9.1 on vegbiendev), so the PL/Python prefix must be optional. Refactored to put IF clause for non-PL/Python exception at end for a more logical ordering of the conditions.
sql_gen.py: plpythonu_error_handler: Fixed bug where not all PL/Python exceptions start with "PL/Python: " (e.g. on PostgreSQL 9.1 on vegbiendev), so the PL/Python prefix must be optional. Refactored to put IF clause for non-PL/Python exception at end for a more logical ordering of the conditions.