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

db_xml.py: put_table(): Divide fields into input columns and literal values: Translate values: Allow literal values other than strings or None (from the XML parsing), because sql_io.put_table() is getting an optimization for iterations containing only literal values, which just returns the pkey of the single row for these values (which is usually an integer) instead of a temp table with the same value in each row

bin/map: by_col: Stripping XML functions not in the DB: Remove DB functions based on whether a plain SQL function of that name exists, rather than whether a relational function (i.e. a table) of that name exists. This will allow column-based import to use plain SQL functions that don't have a corresponding relational function.

db_xml.py: Don't remove any explicit pkey because the output table may be a SQL function, which does not have a pkey. This feature only existed to support importing VegBank XML exports, which we don't use (and which would be incompatible with the schema anyway).

sql.py: function_exists(): Fixed bug where select() needed to be run with auto-rollback in case it raised an exception

xml_func.py: process(): Changed rel_funcs param to a callback is_rel_func, so that caller can specify any dynamic function to determine if a name is a relational function rather than having to list out all known relational functions

sql.py: function_exists(): Use simpler cast to regproc instead of query of information_schema.routines to determine if function exists. When the schema is not specified, this also limits the schemas checked to the search_path instead of the whole DB.

schemas/functions.sql, py_functions.sql: Renamed trigger functions to avoid collisions with plain SQL functions of the same name but different signatures, so that the plain SQL functions can be uniquely identified by their name without also requiring their signature