FTS Configuration option

Hello hackers,

Sometimes there is a need to collect lexems from various dictionaries.
For example, if we have a column with text in various languages.

Let's say there is a new option JOIN. This option will allow to the
parser to append lexems from the current dictionary and go to the next
dictionary:

=> CREATE TEXT SEARCH CONFIGURATION multi_conf (COPY=simple);
=> ALTER TEXT SEARCH CONFIGURATION multi_conf
ALTER MAPPING FOR asciiword, asciihword, hword_asciipart,
word, hword, hword_part
WITH german_ispell (JOIN), english_ispell, simple;

Here there are the following cases:
- found lexem in german_ispell, didn't found lexem in english_ispell.
Return lexem from german_ispell.
- didn't found lexem in german_ispell, found lexem in english_ispell.
Return lexem from english_ispell.
- didn't found lexems in dictionaries. Return lexem from simple.
- found lexems in both dictionaries. Return lexems from both.

Could be such option is useful to the community? Name of the option is
debatable.

Thank you!

--
Artur Zakirov
Postgres Professional: http://www.postgrespro.com
Russian Postgres Company