Fix inconsistencies and typos in the tree

This is numbered take 7, and addresses a set of issues with code
comments, variable names and unreferenced variables.

Author: Alexander Lakhin
Discussion: https://postgr.es/m/dff75442-2468-f74f-568c-6006e141062f@gmail.com

src/backend/access/hash/hashovfl.c

@@ -793,7 +793,7 @@ _hash_initbitmapbuffer(Buffer buf, uint16 bmsize, bool initpage)
  *	be confused into returning the same tuple more than once or some tuples
  *	not at all by the rearrangement we are performing here.  To prevent
  *	any concurrent scan to cross the squeeze scan we use lock chaining
- *	similar to hasbucketcleanup.  Refer comments atop hashbucketcleanup.
+ *	similar to hashbucketcleanup.  Refer comments atop hashbucketcleanup.
  *
  *	We need to retain a pin on the primary bucket to ensure that no concurrent
  *	split can start.

src/backend/access/hash/hashpage.c

@@ -509,7 +509,7 @@ _hash_init_metabuffer(Buffer buf, double num_tuples, RegProcedure procid,
 	 * Choose the number of initial bucket pages to match the fill factor
 	 * given the estimated number of tuples.  We round up the result to the
 	 * total number of buckets which has to be allocated before using its
-	 * _hashm_spare element. However always force at least 2 bucket pages. The
+	 * hashm_spares element. However always force at least 2 bucket pages. The
 	 * upper limit is determined by considerations explained in
 	 * _hash_expandtable().
 	 */