inputs/SALVIAS*/maps/VegX.plots.csv: Updated _units for % -> decimal conversion to use new syntax

inputs/SALVIAS*/maps/VegX.plots.csv: Updated _units for % -> decimal conversion to use new syntax

xml_func.py: _units: If value can't be converted to float, wrap the ValueError in a SyntaxException

units.py: convert(): Added support for unit conversions. Added initial unit conversion for % -> unitless. str2quantity(): Fixed regexp to match % as units. Set Quantity.__repr__ to quantity2str.

units.py: convert(): Put "units None" test after "quantity.units units" test because a destination of no units might require a conversion for some input units (e.g. % -> unitless requires a division by 100)

inputs/SALVIAS*/maps/VegX.organisms.csv: Habit: Ignore invalid values instead of generating a SyntaxException

xml_dom.py: minidom modifications: Escape as many text strings as we use directly. This still leaves the tagName used by xml.dom.minidom.Element.writexml: It uses 'writer.write(indent+"<" + self.tagName)' and doesn't escape the tagName.

xml_func.py: Made everything Unicode-safe by using strings.ustr instead of str

schemas/tree_cross-links.sql: Added comment for how to get the namedplace trigger from the provided plantname trigger

vegbien.sql: Fixed bug in tree cross-link algorithm where recursion to descendants' ancestors did not use new to refer to the current node's plantname_id