exc.py: Support exception messages containing non-ASCII characters

sql.py: put_table(): Print debug messages about how exceptions are being handled

sql.py: put_table(): After getting pkeys of already existing rows, insert new rows

sql.py: put_table(): Handle FunctionValueExceptions by excluding rows with the invalid value in their "value" column

sql.py: run_query(): Also parse "invalid input syntax at assignment" errors as FunctionValueExceptions

sql_gen.py: Col: Convert string table names to Table objects

sql.py: run_query(): Parse "invalid input value at assignment" errors' values as well

sql.py: run_query(): Parse "invalid input value at assignment" errors as FunctionValueExceptions

sql.py: mk_select(): joins: filter_out: Pass NULLs through. Use sql_gen.*2sql_gen() to add the left and right table names to the columns.

sql_gen.py: cond2sql_gen(): Take assume_col param and pass it to value2sql_gen()