Fix many typos and inconsistencies

Author: Alexander Lakhin
Discussion: https://postgr.es/m/af27d1b3-a128-9d62-46e0-88f424397f44@gmail.com

src/backend/optimizer/path/equivclass.c

@@ -929,11 +929,10 @@ generate_base_implied_equalities_no_const(PlannerInfo *root,
 	/*
 	 * We scan the EC members once and track the last-seen member for each
 	 * base relation.  When we see another member of the same base relation,
-	 * we generate "prev_mem = cur_mem".  This results in the minimum number
-	 * of derived clauses, but it's possible that it will fail when a
-	 * different ordering would succeed.  XXX FIXME: use a UNION-FIND
-	 * algorithm similar to the way we build merged ECs.  (Use a list-of-lists
-	 * for each rel.)
+	 * we generate "prev_em = cur_em".  This results in the minimum number of
+	 * derived clauses, but it's possible that it will fail when a different
+	 * ordering would succeed.  XXX FIXME: use a UNION-FIND algorithm similar
+	 * to the way we build merged ECs.  (Use a list-of-lists for each rel.)
 	 */
 	prev_ems = (EquivalenceMember **)
 		palloc0(root->simple_rel_array_size * sizeof(EquivalenceMember *));

src/backend/optimizer/plan/createplan.c

@@ -3911,7 +3911,7 @@ create_foreignscan_plan(PlannerInfo *root, ForeignPath *best_path,
 }
 
 /*
- * create_custom_plan
+ * create_customscan_plan
  *
  * Transform a CustomPath into a Plan.
  */

src/backend/optimizer/util/clauses.c

@@ -3409,10 +3409,10 @@ eval_const_expressions_mutator(Node *node,
 			{
 				/*
 				 * This case could be folded into the generic handling used
-				 * for ArrayRef etc.  But because the simplification logic is
-				 * so trivial, applying evaluate_expr() to perform it would be
-				 * a heavy overhead.  BooleanTest is probably common enough to
-				 * justify keeping this bespoke implementation.
+				 * for SubscriptingRef etc.  But because the simplification
+				 * logic is so trivial, applying evaluate_expr() to perform it
+				 * would be a heavy overhead.  BooleanTest is probably common
+				 * enough to justify keeping this bespoke implementation.
 				 */
 				BooleanTest *btest = (BooleanTest *) node;
 				BooleanTest *newbtest;