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

mappings/DwC2-VegBIEN.specimens.csv: *Latitude/*Longitude: Moved _toDouble directly after the output col name, so that it's run after any translation functions (which all return strings). *ElevationInMeters: Added _toDouble around all output cols.

xpath.py: get(): Create attrs: Fixed bug where attrs were created with last_only on, which caused attrs to get created multiple times if there were multiple attrs of the same name but different values, becase the last_only optimization would only check the last attr of that name