pgsql: Back-patch 8.2 fix that complains if trying to extend a relation

Log Message:
-----------
Back-patch 8.2 fix that complains if trying to extend a relation encounters
a buffer containing a non-zeroed page.  This seems appropriate now that the
8.2 fix has been seen to save at least one user from data loss due to a
buggy kernel (per report from Jaime Silvela 7-May-07).  I'd go further
back than 8.1, except that the 8.0-to-8.1 bufmgr changes are large
enough that the patch doesn't work immediately; I'm hesitant to make a
change without more extensive analysis than I have time for now.

Tags:
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REL8_1_STABLE

Modified Files:
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    pgsql/src/backend/storage/buffer:
        bufmgr.c (r1.198.2.3 -> r1.198.2.4)

(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/storage/buffer/bufmgr.c.diff?r1=1.198.2.3&r2=1.198.2.4)