[PATCH] Pageinspect - add functions on GIN and GiST indexes from gevel

Hi all,

the following patch transfers functionality from gevel module
(http://www.sai.msu.su/~megera/wiki/Gevel) which provides functions for
analyzing GIN and GiST indexes to pageinspect. Gevel was originally
designed by Oleg Bartunov, and Teodor Sigaev for developers of GiST and
GIN indexes.

Functions added:
- gist_stat(text) - shows statistics on GiST Tree
- gist_tree(text) - shows GiST tree
- gist_tree(text, int4) - shows GiST tree up to MAXLEVEL
- gist_print(text) - prints objects stored in GiST tree
- spgist_stat(text) - shows statistics on SP-GiST
- spgist_print(text) - prints objects stored in index
- gin_value_count() - originally gin_stat(text) - prints estimated counts
for index values
- gin_stats() - originally gin_statpage(text) - shows statistics
- gin_count_estimate(text, tsquery) - shows number of indexed rows matched
query

Tests also transferred, docs for new functions are added. I run pgindent
over the code, but the result is different from those I expected, so I leave
pgindented one.
The patch is applicable to the commit
866f4a7c210857aa342bf901558d170325094dde.

--
Alexey Chernyshov
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company