Fix misc typos.

Oskari Saarenmaa. Backpatch to stable branches where applicable.

src/backend/access/heap/heapam.c

@@ -5473,7 +5473,7 @@ l4:
  *
  * The initial tuple is assumed to be already locked.
  *
- * This function doesn't check visibility, it just inconditionally marks the
+ * This function doesn't check visibility, it just unconditionally marks the
  * tuple(s) as locked.  If any tuple in the updated chain is being deleted
  * concurrently (or updated with the key being modified), sleep until the
  * transaction doing it is finished.
@@ -6187,7 +6187,7 @@ heap_prepare_freeze_tuple(HeapTupleHeader tuple, TransactionId cutoff_xid,
 			/*
 			 * NB -- some of these transformations are only valid because we
 			 * know the return Xid is a tuple updater (i.e. not merely a
-			 * locker.) Also note that the only reason we don't explicitely
+			 * locker.) Also note that the only reason we don't explicitly
 			 * worry about HEAP_KEYS_UPDATED is because it lives in
 			 * t_infomask2 rather than t_infomask.
 			 */

src/backend/access/heap/rewriteheap.c

@@ -763,9 +763,9 @@ raw_heap_insert(RewriteState state, HeapTuple tup)
  *
  * Crash-Safety: This module diverts from the usual patterns of doing WAL
  * since it cannot rely on checkpoint flushing out all buffers and thus
- * waiting for exlusive locks on buffers. Usually the XLogInsert() covering
+ * waiting for exclusive locks on buffers. Usually the XLogInsert() covering
  * buffer modifications is performed while the buffer(s) that are being
- * modified are exlusively locked guaranteeing that both the WAL record and
+ * modified are exclusively locked guaranteeing that both the WAL record and
  * the modified heap are on either side of the checkpoint. But since the
  * mapping files we log aren't in shared_buffers that interlock doesn't work.
  *