small but useful patches for text search

Hi there,

I and Teodor have several small, but useful patches for text search:

1. Support of filtering dictionaries and unaccent dictionary/function.
This is often requested feature, which solves, for example,
problem with correct headlines for text with accents.
See example and docs http://www.sai.msu.su/~megera/wiki/unaccent

2. Add prefix search support to the synonym dictionary.
Star sign '*' at the end of definition word indicates,
that definition word is a prefix and to_tsquery() function will transform
that definition to the prefix search format.
Notice, it is ignored in to_tsvector().
Some examples http://www.sai.msu.su/~megera/wiki/2009-03-13

There are limitations - no support for thesaurus dictionary,
ts_debug doesn't support all these features (it needs to be rewritten
to C).

There is no problem with back compatibility.

We would like to have your opinion what to do with these patches - leave them
for 8.5 or provide them to hackers to review for 8.4.

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