backups/Makefile: Added %.backup/rotate

backups/Makefile: Rearranged sections so that backup targets, which apply to both Archived imports and Full DB, are at the top of a common Backups section

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

schemas/py_functions.sql: Disabled _date() because it does not yet output errors in a format parsable by the import process, and the import process does not yet trap errors produced by SQL functions

sql_io.py: put_table(): Determining if can use optimization for only literal values: Fixed bug where needed initial value for reduce()

sql_io.py: put_table(): Needing >= one column for INSERT SELECT: Fixed bug where can't add pkey column if calling a function instead of outputting to a table

sql_io.py: put_table(): Optimization for only literal values: Also support an empty in_tables list, for use by put()

sql_io.py: put_table(): Added optimization for only literal values, which does the same operations as put() but with the additional error handling of put_table()

pg_dump_vegbien: Don't use SET SESSION AUTHORIZATION because it doesn't work with the py_functions schema (it requires PL/Python functions to be created as user postgres and then the owner changed to bien, which SET SESSION AUTHORIZATION won't do)

sql_gen.py: Added is_literal() and use it where isinstance(..., Literal) is used