EXPLAIN and nfiltered

Hi,

Here's a patch for showing in EXPLAIN ANALYZE the number of rows a plan
qual filtered from a node's input. The output looks like this:

QUERY PLAN

-----------------------------------------------------------------------------------------------------------------------
Subquery Scan on ss (cost=0.00..50.00 rows=267 width=4) (actual
time=0.035..0.088 rows=5 filtered=3 loops=1)
Filter: (ss.a < 6)
-> Limit (cost=0.00..40.00 rows=800 width=4) (actual
time=0.031..0.067 rows=8 filtered=0 loops=1)
-> Seq Scan on foo (cost=0.00..40.00 rows=800 width=4)
(actual time=0.027..0.040 rows=8 filtered=2 loops=1)
Filter: (a < 9)
Total runtime: 0.146 ms
(6 rows)

It might be better if the output was on the Filter: line but this was
just the result of a quick idea and I wanted to see how much work the
actual implementation would be.

Any suggestions and comments on the output format, the patch and the
idea are welcome.

Regards,
Marko Tiikkaja