Fix various typos

This fixes many spelling mistakes in comments, but a few references to
invalid parameter names, function names and option names too in comments
and also some in string constants

Also, fix an #undef that was undefining the incorrect definition

Author: Alexander Lakhin
Reviewed-by: Justin Pryzby
Discussion: https://postgr.es/m/d5f68d19-c0fc-91a9-118d-7c6a5a3f5fad@gmail.com

src/backend/storage/buffer/bufmgr.c

@@ -2046,7 +2046,7 @@ ExtendBufferedRelShared(ExtendBufferedWhat eb,
 	io_start = pgstat_prepare_io_time();
 
 	/*
-	 * Note: if smgzerorextend fails, we will end up with buffers that are
+	 * Note: if smgrzeroextend fails, we will end up with buffers that are
 	 * allocated but not marked BM_VALID.  The next relation extension will
 	 * still select the same block number (because the relation didn't get any
 	 * longer on disk) and so future attempts to extend the relation will find

src/backend/storage/lmgr/predicate.c

@@ -164,7 +164,7 @@
  *		PredicateLockPage(Relation relation, BlockNumber blkno,
  *						Snapshot snapshot)
  *		PredicateLockTID(Relation relation, ItemPointer tid, Snapshot snapshot,
- *						 TransactionId insert_xid)
+ *						 TransactionId tuple_xid)
  *		PredicateLockPageSplit(Relation relation, BlockNumber oldblkno,
  *							   BlockNumber newblkno)
  *		PredicateLockPageCombine(Relation relation, BlockNumber oldblkno,

src/backend/storage/smgr/md.c

@@ -597,7 +597,7 @@ mdzeroextend(SMgrRelation reln, ForkNumber forknum,
 			/*
 			 * Even if we don't want to use fallocate, we can still extend a
 			 * bit more efficiently than writing each 8kB block individually.
-			 * pg_pwrite_zeroes() (via FileZero()) uses
+			 * pg_pwrite_zeros() (via FileZero()) uses
 			 * pg_pwritev_with_retry() to avoid multiple writes or needing a
 			 * zeroed buffer for the whole length of the extension.
 			 */