join: Added new passthru mode which passes through terms with no input mapping or no join mapping

inputs/: Added [Veg+] to via map roots to indicate that the datasource and Veg+ vocabularies are combinable. This is possible now that automapped entries are no longer subtracted when this is in the map root, so there is no concern of losing comments on subtracted automapped rows. Note that this change turns on old-style automapping for these datasources, causing SALVIAS plotMetadata to acquire additional mappings.

canon, translate, filter_out_ci: Support vocabularies/dictionaries with additional columns in addition to the functional column(s) used by the program. These columns can contain comments, etc. This was not originally supported because Python 2's iterable unpacking only supports "an iterable with the same number of items as there are targets in the target list" (http://docs.python.org/reference/simple_stmts.html#assignment-statements). We now use numeric array indexes instead to get around this limitation, and for consistency with other map-manipulation scripts.

Removed no longer used subtract (use filter_out_ci instead)

input.Makefile: Maps building: %/.map.csv.last_cleanup: Removed no longer needed subtraction of automapped entries, because information about unmapped and new terms is now available in unmapped_terms.csv and new_terms.csv

README.TXT: Data import: `make backups/download`: Removed '&' because running the command in the background prevents rsync from providing a continuously updating progress indication (because a backgrounded process's stdout is not a TTY)

mappings/VegCore-VegBIEN.csv: Removed no longer needed /_simplifyPath:[next=parent_id]/path expressions in specific paths because parent_id forwarding is now set globally for all paths in the map root

mappings/VegCore-VegBIEN.csv: Added /_simplifyPath:[next=parent_id]/path to root so the returned subplot location will be its parent location if there is no subplot name or ID (indicating that that particular plot did not have subplots). Note that this also causes the parent_id forwarding effect to occur for all other tables containing parent_id, which will help prevent similar issues with subplot events, etc. This will hopefully fix the SALVIAS.plotObservations bug where some organisms did not have a subplot #, causing the subplot location to become NULL and causing the corresponding locationevent rows not to match the locationevent_unique_within_location index filter condition (which requires a parent_id), which caused multiple output table pkeys to be returned for those rows, violating the locationevent_pkeys temp table's primary key.

mappings/VegCore-VegBIEN.csv: namedplace elements: _simplifyPath() calls: Removed no longer needed `require` arg, and removed no longer needed table suffix from `next` arg

inputs/import.stats.xls: Updated with stats from latest import