strings.py: Added raw_extra_len()

sql_gen.py: NoUnderlyingTableException: Take a (required) parameter for the item that had no underlying table, and provide this wherever a NoUnderlyingTableException is created

strings.py: concat(): Perform substring operation on Unicode strings so that substring does not split Unicode characters. Still use to_raw_str() to calculate the str1 length because Unicode characters can be multi-byte, and length limits often apply to the byte length, not the character length.

exc.py: add_msg(): Fixed bug where needed to convert the Unicode string back into a raw string because Python's top-level exception handler doesn't support Unicode strings as exception messages

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

inputs: Renamed stems table to 2.stems so import order would be inherent in the dir name, using steps at <https://projects.nceas.ucsb.edu/nceas/projects/bien/wiki/VegCSV_subfolders#Rename-subfolders-with-import-order>

inputs: Renamed organisms table to 1.organisms so import order would be inherent in the dir name, using steps at <https://projects.nceas.ucsb.edu/nceas/projects/bien/wiki/VegCSV_subfolders#Rename-subfolders-with-import-order>

inputs: Renamed plots table to 0.plots so import order would be inherent in the dir name, using steps at <https://projects.nceas.ucsb.edu/nceas/projects/bien/wiki/VegCSV_subfolders#Rename-subfolders-with-import-order>

inputs: Renamed plots table to 0.plots so import order would be inherent in the dir name, using steps at <https://projects.nceas.ucsb.edu/nceas/projects/bien/wiki/VegCSV_subfolders#Rename-subfolders-with-import-order>

input.Makefile: Mapping: If table subdir contains no input files, print warning instead of aborting. This situation occurs when renaming a version-controlled directory, whose previous version persists as an empty dir until committing.