Prefix support for synonym dictionary

Hi there,

attached is our patch for CVS HEAD, which adds prefix support for synonym
dictionary.

Quick example:

> cat $SHAREDIR/tsearch_data/synonym_sample.syn
postgres pgsql
postgresql pgsql
postgre pgsql
gogle googl
indices index*

=# create text search dictionary syn( template=synonym,synonyms='synonym_sample');
=# select ts_lexize('syn','indices');
ts_lexize
-----------
{index}
(1 row)
=# create text search configuration tst ( copy=simple);
=# alter text search configuration tst alter mapping for asciiword with syn;
=# select to_tsquery('tst','indices');
to_tsquery
------------
'index':*
(1 row)
=# select 'indexes are very useful'::tsvector @@ to_tsquery('tst','indices');
?column?
----------
t
(1 row)

Regards,
Oleg
_____________________________________________________________
Oleg Bartunov, Research Scientist, Head of AstroNet (www.astronet.ru)
Sternberg Astronomical Institute, Moscow University, Russia
Internet: oleg(at)sai(dot)msu(dot)su, http://www.sai.msu.su/~megera/
phone: +007(495)939-16-83, +007(495)939-23-83