BUG #3798: Add fuzzy string search in TSearch2

The following bug has been logged online:

Bug reference:      3798
Logged by:          Rikardo Tinauer
Email address:      rikardo.tinauer@eba.si
PostgreSQL version: 8.3
Operating system:   All
Description:        Add fuzzy string search in TSearch2
Details:

This is not really a bug but just an idea I saw on IBM DB2. They have the
capability to do the fuzzy search on full text indexes.

It would be great to have this in PostgreSQL.

We are developers of Documents System, out primary dateabase is Postgres and
many of our major customers (large companies) use our DMS on Postgres (by
the way excellent database you guys develop). Since scanning is one of
possibilities how to get document into DMS we thought it would be great if
one could search the words of scanned document (we perform OCR on document).
But OCR recognized words aren't fully trustworthy (they have errors), so
fuzzy search would eliminate them since searching on word 'invoice' would
also return hits with words like 'inv0ice' etc...