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_2_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/a1c3d54fb6b9fd974fa4d0166bfd1fde30c8d8c2

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