specimens verification: Added # counties test

specimens verification: Added collection codes and # catalog numbers tests

inputs/SALVIAS/maps/VegX.organisms.csv: Mapped custom Habit values not listed in the SALVIAS data dictionary

strings.py: Added unicode_reader for later use in handling Unicode characters in map spreadsheets

xpath.py: Removed unnecessary copy.deepcopy()'s and instead changed set_value() and set_id() to make copies of any elements they change. This should result in up to a 17% speed increase in the import, because deepcopy() was taking a lot of time. Added documentation to set_value() and set_id() that caller must make a shallow copy of the path to prevent modifications from propagating to other copies of the path. (Previously, a deep copy was needed, but there was no comment specifying this.)

mappings/VegX-VegBIEN.organisms.csv: Removed unneeded lookahead assertions from stemtag mappings. They relied on a bug ("feature"?) in the XPath engine that made the value of the lookahead assertion's path the same as the value of the main path, even though the value is set after the path is parsed.

xml_func.py: _date: For year/month/day dates, require the year (it would not make sense to default to a particular year)

inputs/UArizona: Added test outputs

mappings/DwC1-DwC2.specimens.csv: Fixed to allow datasource to define custom date mappings that don't pass through the default date mapping

input.Makefile: Generate maps/src.join.*.csv, which can be used to determine which DwC fields for a particular dataset do not yet have a join mapping to VegBIEN