pgsql: Retry after buffer locking failure during SPGiST index creation.

Retry after buffer locking failure during SPGiST index creation.

The original coding thought this case was impossible, but it can happen
if the bgwriter or checkpointer processes decide to write out an index
page while creation is still proceeding, leading to a bogus "unexpected
spgdoinsert() failure" error.  Problem reported by Jonathan S. Katz.

Teodor Sigaev

Branch
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REL9_3_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/86dab9c8addd2898abc0feddc4e7f1ef0cd786f4

Modified Files
--------------
src/backend/access/spgist/spgdoinsert.c |    9 ++++++---
src/backend/access/spgist/spginsert.c   |   15 +++++++++++----
2 files changed, 17 insertions(+), 7 deletions(-)