bin/map: If out_is_db, in debug mode, print the template XML tree used to insert a sample row into the DB

bin/map: map_table(): When translating mappings to column indexes, use appends to a new list instead of deletions from an existing list to simplify the algorithm

union: Omit mappings that are mapped to in the input map, in addition to mappings that were overridden. This prevents multiple outputs being created for both the renamed and original mappings, causing duplicate output nodes when one XML tree is used for all rows.

union: Omit mappings that are mapped to in the input map, in addition to mappings that were overridden. This prevents multiple outputs being created for both the renamed and original mappings, causing duplicate output nodes when one XML tree is used for all rows.

input.Makefile: Maps building: Via maps cleanup: subtract: Include comment column so commented mappings are never removed

subtract: Support "ragged rows" that have fewer columns than the specified column numbers

util.py: list_subset(): Added default param to specify the value to use for invalid indexes (if any)

mappings/VegX-VegBIEN.stems.csv: Mappings with multiple inputs for the same output: Use _alt, etc. to map the multiple inputs to different places in the XML tree, so that when using a pregenerated tree, the empty leaves for each input will not collide with each other

mappings/VegX-VegBIEN.stems.csv: Changed XPath references (using "$") to XML function references using _ref where needed to make them work even on a pre-made XML tree used by all rows

xml_func.py: Added _ref to retrieve a value from another XML node