sql.py: put_table(): Log "Default value column does not exist in mapping" error with level 2.1 so that it doesn't appear in Redmine output

db_xml.py: put_table(): Pass next as sql.put_table()'s default param now that it is supported

sql.py: put_table(): Changed default param to be an output column because that is what would be passed in by db_xml.put_table(), and because there is already a mapping that resolves that to a flattened input column

sql.py: put_table(): Added default param for the value or input column to use as the pkey for missing rows

sql.py: put_table(): Use single quotes rather than double quotes around strings where possible

db_xml.py: Added internal next param used by simplifyPath. put_table(): Refactored to use outer parent_ids_loc var and modify that as needed rather than having to pass parent_ids_loc as a param to put_table_().

sql.py: put_table(): When calling strings.as_*table(), pass custom ustr that removes col renames and adds double quotes on plain strings

strings.py: as_*table(): Added ustr param to override the method (by default ustr()) used to convert each value to a string

sql_gen.py: MockDb.esc_value(): Use new strings.repr_no_u()

strings.py: Added repr_no_u()