pgsql: Back-patch recent fixes for gistchoose and gistRelocateBuildBuff

Back-patch recent fixes for gistchoose and gistRelocateBuildBuffersOnSplit.

This back-ports commits c8ba697a4bdb934f0c51424c654e8db6133ea255 and
e5db11c5582b469c04a11f217a0f32c827da5dd7, which fix one definite and one
speculative bug in gistchoose, and make the code a lot more intelligible as
well. In 9.2 only, this also affects the largely-copied-and-pasted logic
in gistRelocateBuildBuffersOnSplit.

The impact of the bugs was that the functions might make poor decisions
as to which index tree branch to push a new entry down into, resulting in
GiST index bloat and poor performance. The fixes rectify these decisions
for future insertions, but a REINDEX would be needed to clean up any
existing index bloat.

Alexander Korotkov, Robert Haas, Tom Lane

Branch
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REL9_0_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/1da2a610d7e791e93fcf835855badaeb11196bdd

Modified Files
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src/backend/access/gist/gistutil.c | 98 ++++++++++++++++++++++++++---------
1 files changed, 73 insertions(+), 25 deletions(-)