pgsql: Revert "Convert contrib/seg's bool-returning SQL functions to V1

Revert "Convert contrib/seg's bool-returning SQL functions to V1 call convention."

This reverts commit c8e81afc60093b199a128ccdfbb692ced8e0c9cd.
That turns out to have been based on a faulty diagnosis of why the
VS2015 build was misbehaving.  Instead, we need to fix DatumGetBool().

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/f050423052bc9265d4cd27555058435edd4bef87

Modified Files
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contrib/seg/seg.c | 300 +++++++++++++++++++-----------------------------------
1 file changed, 105 insertions(+), 195 deletions(-)