pgsql: Fix documentation oversights about pageinspect and initializatio

Fix documentation oversights about pageinspect and initialization fork.

The initialization fork was added in 9.1, but has not been taken into
consideration in documents of get_raw_page function in pageinspect and
storage layout. This commit fixes those oversights.

get_raw_page can read not only a table but also an index, etc. So it
should be documented that the function can read any relation. This commit
also fixes the document of pageinspect that way.

Back-patch to 9.1 where those oversights existed.

Vik Fearing, review by MauMau

Branch
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REL9_1_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/b8eaa7b2a67c9f9f6730376056903feb3da58293

Modified Files
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doc/src/sgml/pageinspect.sgml | 7 ++++---
doc/src/sgml/storage.sgml | 4 ++--
2 files changed, 6 insertions(+), 5 deletions(-)