it seems taht the query parser do the job for mysql not for pgsql :
operators in tsearch query are : () ! | & but + and - are used
I have patch include/SearchPostgres.php to rewrite using the above operators (I have made some tests,
but not all ....).
Know issue : if you search only by the absence of a word there is strange behaviour (I think this is
more mediawiki code than specific postgresql code)