proposal: additional error fields

Hello

I have to goals for 9.3. First goal is plpgsql_check_function, second
goal is enhancing ErrorData and error management to support new
fields: COLUMN_NAME, CONSTRAINT_NAME, CONSTRAINT_SCHEMA, SCHEMA_NAME,
TABLE_NAME, ROUTINE_NAME, ROUTINE_SCHEMA, TRIGGER_NAME and
TRIGGER_SCHEMA

previous discussion is in thread
http://postgresql.1045698.n5.nabble.com/patch-for-9-2-enhanced-errors-td4470837.html

COLUMN_NAME - contains missing or inaccessible column name or empty string
CONSTRAINT_NAME - a name of constraint caused error
CONSTRAINT_SCHEMA - a name of schema where constraint is defined -
usually same as table schema in PostgreSQL
SCHEMA_NAME - schema name of table that caused exception
ROUTINE_NAME, ROUTINE_SCHEMA name and schema of function that caused
exception - this doesn't mean function where exception was raised
TABLE_NAME - a name of table that caused exception
TRIGGER_NAME, TRIGGER_SCHEMA - name and schema of trigger that caused exception

attached patch is redesigned previous version - actually it supports
constraints and RI only

second patch will be related to plpgsql enhancing to use these error fields.

Regards

Pavel