Report the number of skipped frozen pages by manual VACUUM

Hi all,

The autovacuum reports the number of skipped frozen pages to the
VACUUM output. But these information is not appeared by manual VACUUM.
This information is useful for the user to check efficiency of VACUUM.

Attached patch add this information to VACUUM output.

* Example
=# VACUUM VERBOSE test
INFO:  vacuuming "public.test"
INFO:  "test": found 0 removable, 56 nonremovable row versions in 1
out of 45 pages
DETAIL:  0 dead row versions cannot be removed yet.
There were 0 unused item pointers.
Skipped 0 pages due to buffer pins, 44 frozen pages.
0 pages are entirely empty.
CPU: user: 0.00 s, system: 0.00 s, elapsed: 0.00 s.
VACUUM

I'll register it to next CF.

Regards,

--
Masahiko Sawada
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center