New features for tsearch2:

1 Comparison operation for tsquery
2 Btree index on tsquery
3 numnode(tsquery) - returns 'length' of tsquery
4 tsquery @ tsquery, tsquery ~ tsquery - contains, contained for tsquery.
  Note: They don't gurantee exact result, only MAY BE, so it
  useful only for speed up rewrite functions
5 GiST index support for @,~
6 rewrite():
        select rewrite(orig, what, to);
        select rewrite(ARRAY[orig, what, to]) from tsquery_table;
        select rewrite(orig, 'select what, to from tsquery_table;');
7 significantly improve cover algorithm

contrib/tsearch2/query.h

@@ -17,7 +17,7 @@ typedef struct ITEM
 	int4		val;
 	/* user-friendly value, must correlate with WordEntry */
 	uint32
-				unused:1,
+				istrue:1, /* use for ranking in Cover */
 				length:11,
 				distance:20;
 }	ITEM;