pgsql: Fix failure to mark init buffers as BM_PERMANENT.

Fix failure to mark init buffers as BM_PERMANENT.

This could result in corruption of the init fork of an unlogged index
if the ambuildempty routine for that index used shared buffers to
create the init fork, which was true for brin, gin, gist, and hash
indexes.

Patch by me, based on an earlier patch by Michael Paquier, who also
reviewed this one. This also incorporates an idea from Artur
Zakirov.

Discussion: http://postgr.es/m/CACYUyc8yccE4xfxhqxfh_Mh38j7dRFuxfaK1p6dSNAEUakxUyQ@mail.gmail.com

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/87f99820349bbb020d1d65dd739a910c6f9c813b

Modified Files
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src/backend/storage/buffer/bufmgr.c | 7 ++++++-
src/include/storage/buf_internals.h | 4 ++--
2 files changed, 8 insertions(+), 3 deletions(-)