Fix typos.

Oskari Saarenmaa

src/backend/storage/ipc/dsm_impl.c

@@ -34,7 +34,7 @@
  * substantially, but there should be few systems where we must make do
  * with such poor tools.
  *
- * As ever, Windows requires its own implemetation.
+ * As ever, Windows requires its own implementation.
  *
  * Portions Copyright (c) 1996-2016, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California

src/backend/storage/ipc/procarray.c

@@ -71,7 +71,7 @@ typedef struct ProcArrayStruct
 	 * Known assigned XIDs handling
 	 */
 	int			maxKnownAssignedXids;	/* allocated size of array */
-	int			numKnownAssignedXids;	/* currrent # of valid entries */
+	int			numKnownAssignedXids;	/* current # of valid entries */
 	int			tailKnownAssignedXids;	/* index of oldest valid element */
 	int			headKnownAssignedXids;	/* index of newest element, + 1 */
 	slock_t		known_assigned_xids_lck;		/* protects head/tail pointers */

src/backend/storage/ipc/shm_mq.c

@@ -1104,7 +1104,7 @@ shm_mq_inc_bytes_read(volatile shm_mq *mq, Size n)
 	sender = mq->mq_sender;
 	SpinLockRelease(&mq->mq_mutex);
 
-	/* We shoudn't have any bytes to read without a sender. */
+	/* We shouldn't have any bytes to read without a sender. */
 	Assert(sender != NULL);
 	SetLatch(&sender->procLatch);
 }