sql.py: mk_select(): Support ORDER BY clause. By default, order by the pkey, since PostgreSQL apparently doesn't do this automatically (and this was causing some staging table tests to fail).

bin/map: In debug mode, print the row # and input row just like in error messages

bin/map: verbose_errors also defaults to on in debug mode

sql.py: add_row_num(): Make the row number column the primary key

csv2db: Use new sql.cleanup_table() to map NULL-equivalents to NULL. Consider the empty string to be NULL.

sql.py: Added cleanup_table()

csvs.py: Added row filters

db_xml.py: put_table(): Fixed bug where relational functions were not being treated as value nodes, and thus their containing child was treated as a child with a backwards pointer instead of a field

xml_func.py: Added is_func*() and is_xml_func*() and use them where their definitions were used

db_xml.py: Added value() and use it where xml_dom.first_elem() was used