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@mail.gmail.com>

Author: tglsfdc

doc/src/sgml/func.sgml

@@ -659,7 +659,7 @@
         <literal><function>ceil(<type>dp</type> or <type>numeric</type>)</function></literal>
        </entry>
        <entry>(same as input)</entry>
-       <entry>smallest integer not less than argument</entry>
+       <entry>nearest integer greater than or equal to argument</entry>
        <entry><literal>ceil(-42.8)</literal></entry>
        <entry><literal>-42</literal></entry>
       </row>
@@ -672,7 +672,7 @@
         <literal><function>ceiling(<type>dp</type> or <type>numeric</type>)</function></literal>
        </entry>
        <entry>(same as input)</entry>
-       <entry>smallest integer not less than argument (alias for <function>ceil</function>)</entry>
+       <entry>nearest integer greater than or equal to argument (same as <function>ceil</function>)</entry>
        <entry><literal>ceiling(-95.3)</literal></entry>
        <entry><literal>-95</literal></entry>
       </row>
@@ -725,7 +725,7 @@
         <literal><function>floor(<type>dp</type> or <type>numeric</type>)</function></literal>
        </entry>
        <entry>(same as input)</entry>
-       <entry>largest integer not greater than argument</entry>
+       <entry>nearest integer less than or equal to argument</entry>
        <entry><literal>floor(-42.8)</literal></entry>
        <entry><literal>-43</literal></entry>
       </row>

src/include/catalog/pg_proc.h

@@ -411,11 +411,11 @@ DESCR("round to nearest integer");
 DATA(insert OID = 229 (  dtrunc			   PGNSP PGUID 12 1 0 0 0 f f f f t f i 1 0 701 "701" _null_ _null_ _null_ _null_ _null_	dtrunc _null_ _null_ _null_ ));
 DESCR("truncate to integer");
 DATA(insert OID = 2308 ( ceil			   PGNSP PGUID 12 1 0 0 0 f f f f t f i 1 0 701 "701" _null_ _null_ _null_ _null_ _null_	dceil _null_ _null_ _null_ ));
-DESCR("smallest integer >= value");
+DESCR("nearest integer >= value");
 DATA(insert OID = 2320 ( ceiling		   PGNSP PGUID 12 1 0 0 0 f f f f t f i 1 0 701 "701" _null_ _null_ _null_ _null_ _null_	dceil _null_ _null_ _null_ ));
-DESCR("smallest integer >= value");
+DESCR("nearest integer >= value");
 DATA(insert OID = 2309 ( floor			   PGNSP PGUID 12 1 0 0 0 f f f f t f i 1 0 701 "701" _null_ _null_ _null_ _null_ _null_	dfloor _null_ _null_ _null_ ));
-DESCR("largest integer <= value");
+DESCR("nearest integer <= value");
 DATA(insert OID = 2310 ( sign			   PGNSP PGUID 12 1 0 0 0 f f f f t f i 1 0 701 "701" _null_ _null_ _null_ _null_ _null_	dsign _null_ _null_ _null_ ));
 DESCR("sign of value");
 DATA(insert OID = 230 (  dsqrt			   PGNSP PGUID 12 1 0 0 0 f f f f t f i 1 0 701 "701" _null_ _null_ _null_ _null_ _null_	dsqrt _null_ _null_ _null_ ));
@@ -2318,11 +2318,11 @@ DESCR("value truncated to 'scale'");
 DATA(insert OID = 1710 ( trunc					PGNSP PGUID 14 1 0 0 0 f f f f t f i 1 0 1700 "1700" _null_ _null_ _null_ _null_ _null_ "select pg_catalog.trunc($1,0)" _null_ _null_ _null_ ));
 DESCR("value truncated to 'scale' of zero");
 DATA(insert OID = 1711 ( ceil					PGNSP PGUID 12 1 0 0 0 f f f f t f i 1 0 1700 "1700" _null_ _null_ _null_ _null_ _null_ numeric_ceil _null_ _null_ _null_ ));
-DESCR("smallest integer >= value");
+DESCR("nearest integer >= value");
 DATA(insert OID = 2167 ( ceiling				PGNSP PGUID 12 1 0 0 0 f f f f t f i 1 0 1700 "1700" _null_ _null_ _null_ _null_ _null_ numeric_ceil _null_ _null_ _null_ ));
-DESCR("smallest integer >= value");
+DESCR("nearest integer >= value");
 DATA(insert OID = 1712 ( floor					PGNSP PGUID 12 1 0 0 0 f f f f t f i 1 0 1700 "1700" _null_ _null_ _null_ _null_ _null_ numeric_floor _null_ _null_ _null_ ));
-DESCR("largest integer <= value");
+DESCR("nearest integer <= value");
 DATA(insert OID = 1718 ( numeric_eq				PGNSP PGUID 12 1 0 0 0 f f f f t f i 2 0 16 "1700 1700" _null_ _null_ _null_ _null_ _null_ numeric_eq _null_ _null_ _null_ ));
 DATA(insert OID = 1719 ( numeric_ne				PGNSP PGUID 12 1 0 0 0 f f f f t f i 2 0 16 "1700 1700" _null_ _null_ _null_ _null_ _null_ numeric_ne _null_ _null_ _null_ ));
 DATA(insert OID = 1720 ( numeric_gt				PGNSP PGUID 12 1 0 0 0 f f f f t f i 2 0 16 "1700 1700" _null_ _null_ _null_ _null_ _null_ numeric_gt _null_ _null_ _null_ ));