mappings: Made VegX-VegBIEN.organisms.csv, VegX-VegBIEN.plots.csv symlinks to VegX-VegBIEN.stems.csv instead of building them in the Makefile by copying VegX-VegBIEN.stems.csv, since these files are now always the same

mappings/VegX-VegBIEN.stems.csv: _if that maps to specimenreplicate via plantobservation or voucher: Refactored to map right-hand side of _eq in the left-hand side mapping, rather than in all then/else mappings. Distinguish this _if statement from others using new name param.

xml_func.py: _if(): Documented that can add `name` param to distinguish separate _if statements

xml_func.py: _if(): Made cond optional. When it's not specified or None, it is treated as False. This supports cases where all elements of the condition are required but not mapped to.

mappings/VegX-VegBIEN.stems.csv: _if that maps to specimenreplicate via plantobservation or voucher: Refactored to map voucherType directly into _if/cond/_eq/left rather than mapping it to a temporary _ignore location and retrieving it with _ref

xml_func.py: Removed no longer used _simplifyPath(), which is now a built-in function of db_xml.put()

xml_func.py: _eq(): Documented that '' (empty node) is returned if a value was not mapped to, not if a value was None, since None arguments are no longer removed by process() (now XML functions do this manually with conv_items())

xml_func.py: _ref(): Only display "XPath reference target missing" warning if target node does not exist, not if it exists but is empty

xpath.py: get(): reference expansion: Use get_1() and check for None result instead of using get(), which returns multiple nodes when we just want the first

mappings/VegX-VegBIEN.stems.csv: Reversed XPaths so that they start with location instead of plantobservation