pgsql: Clarify documentation of ceil/ceiling/floor functions.

Clarify documentation of ceil/ceiling/floor functions.

Document these as "nearest integer >= argument" and "nearest integer <=
argument", which will hopefully be less confusing than the old formulation.
New wording is from Matlab via Dean Rasheed.

I changed the pg_description entries as well as the SGML docs. In the
back branches, this will only affect installations initdb'd in the future,
but it should be harmless otherwise.

Discussion: <CAEZATCW3yzJo-NMSiQs5jXNFbTsCEftZS-Og8=FvFdiU+kYuSA(at)mail(dot)gmail(dot)com>

Branch
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REL9_4_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/d9ce54c0b83506473828444c30a96e3e2601fe7d

Modified Files
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doc/src/sgml/func.sgml | 6 +++---
src/include/catalog/pg_proc.h | 12 ++++++------
2 files changed, 9 insertions(+), 9 deletions(-)