mappings/Makefile: Generate DwC-VegBIEN.specimens.csv directly from DwC1-DwC2 and DwC2-VegBIEN mappings by using join_union_sort with header_num=1, rather than via intermediate DwC1-VegBIEN.specimens.csv
mappings/Makefile: Generate DwC-VegBIEN.specimens.csv directly from DwC1-DwC2 and DwC2-VegBIEN mappings by using join_union_sort with header_num=1, rather than via intermediate DwC1-VegBIEN.specimens.csv