pgsql: Make GiST index searches smarter about queries against empty ran

Make GiST index searches smarter about queries against empty ranges.

In the cases where the result of the called proc is negated, we should
explicitly test both inputs for empty, to ensure we'll never return "true"
for an unsatisfiable query.  In other cases we can rely on the called proc
to say the right thing.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/5966bcecf6167f2921e614e66499fa4d2c195c64

Modified Files
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src/backend/utils/adt/rangetypes_gist.c |   13 +++++++++----
1 files changed, 9 insertions(+), 4 deletions(-)