Clarify descriptions of relhassubclass and relispartition in pg_class

Three places are fixed, one for each author.

Reported-by: Tom Lane
Author: Tom Lane, Amit Langote, Michael Paquier
Discussion: https://postgr.es/m/82470.1540177167@sss.pgh.pa.us

doc/src/sgml/catalogs.sgml

@@ -1900,7 +1900,9 @@ SCRAM-SHA-256$<replaceable>&lt;iteration count&gt;</replaceable>:<replaceable>&l
       <entry><structfield>relhassubclass</structfield></entry>
       <entry><type>bool</type></entry>
       <entry></entry>
-      <entry>True if table has (or once had) any inheritance children</entry>
+      <entry>
+       True if table or index has (or once had) any inheritance children
+      </entry>
      </row>
 
      <row>
@@ -1948,7 +1950,7 @@ SCRAM-SHA-256$<replaceable>&lt;iteration count&gt;</replaceable>:<replaceable>&l
       <entry><structfield>relispartition</structfield></entry>
       <entry><type>bool</type></entry>
       <entry></entry>
-      <entry>True if table is a partition</entry>
+      <entry>True if table or index is a partition</entry>
      </row>
 
      <row>

src/include/catalog/pg_class.h

@@ -60,7 +60,7 @@ CATALOG(pg_class,1259,RelationRelationId) BKI_BOOTSTRAP BKI_ROWTYPE_OID(83,Relat
 	bool		relhasoids;		/* T if we generate OIDs for rows of rel */
 	bool		relhasrules;	/* has (or has had) any rules */
 	bool		relhastriggers; /* has (or has had) any TRIGGERs */
-	bool		relhassubclass; /* has (or has had) derived classes */
+	bool		relhassubclass; /* has (or has had) child tables or indexes */
 	bool		relrowsecurity; /* row security is enabled or not */
 	bool		relforcerowsecurity;	/* row security forced for owners or
 										 * not */