Again update C comments for pg_attribute.attislocal

Author: bmomjian

src/include/catalog/pg_attribute.h

@@ -137,9 +137,13 @@ CATALOG(pg_attribute,1249) BKI_BOOTSTRAP BKI_WITHOUT_OIDS BKI_ROWTYPE_OID(75) BK
 	bool		attisdropped;
 
 	/*
-	 * Has a local definition (hence, do not drop when attinhcount is 0)
-	 * This is set and remains set if the column was _ever_
-	 * local/not-inherited, e.g. this can be set by ALTER TABLE NO INHERIT.
+	 * This flag specifies whether this column has ever had a local
+	 * definition.  It is set for normal non-inherited columns, but also
+	 * for columns that are inherited from parents if also explicitly listed
+	 * in CREATE TABLE INHERITS.  It is also set when inheritance is removed
+	 * from a table with ALTER TABLE NO INHERIT.  If the flag is set, the
+	 * column is not dropped by a parent's DROP COLUMN even if this causes
+	 * the column's attinhcount to become zero.
 	 */
 	bool		attislocal;