Collection of typo fixes.

Use "a" and "an" correctly, mostly in comments. Two error messages were
also fixed (they were just elogs, so no translation work required). Two
function comments in pg_proc.h were also fixed. Etsuro Fujita reported one
of these, but I found a lot more with grep.

Also fix a few other typos spotted while grepping for the a/an typos.
For example, "consists out of ..." -> "consists of ...". Plus a "though"/
"through" mixup reported by Euler Taveira.

Many of these typos were in old code, which would be nice to backpatch to
make future backpatching easier. But much of the code was new, and I didn't
feel like crafting separate patches for each branch. So no backpatching.

src/backend/replication/basebackup.c

@@ -443,7 +443,7 @@ perform_base_backup(basebackup_options *opt, DIR *tblspcdir)
 			/*
 			 * Mark file as archived, otherwise files can get archived again
 			 * after promotion of a new node. This is in line with
-			 * walreceiver.c always doing a XLogArchiveForceDone() after a
+			 * walreceiver.c always doing an XLogArchiveForceDone() after a
 			 * complete segment.
 			 */
 			StatusFilePath(pathbuf, walFiles[i], ".done");

src/backend/replication/logical/logical.c

@@ -149,7 +149,7 @@ StartupDecodingContext(List *output_plugin_options,
 	 * replication slots.
 	 *
 	 * We can only do so if we're outside of a transaction (i.e. the case when
-	 * streaming changes via walsender), otherwise a already setup
+	 * streaming changes via walsender), otherwise an already setup
 	 * snapshot/xid would end up being ignored. That's not a particularly
 	 * bothersome restriction since the SQL interface can't be used for
 	 * streaming anyway.
@@ -225,7 +225,7 @@ CreateInitDecodingContext(char *plugin,
 
 	/* first some sanity checks that are unlikely to be violated */
 	if (slot == NULL)
-		elog(ERROR, "cannot perform logical decoding without a acquired slot");
+		elog(ERROR, "cannot perform logical decoding without an acquired slot");
 
 	if (plugin == NULL)
 		elog(ERROR, "cannot initialize logical decoding without a specified plugin");
@@ -377,7 +377,7 @@ CreateDecodingContext(XLogRecPtr start_lsn,
 
 	/* first some sanity checks that are unlikely to be violated */
 	if (slot == NULL)
-		elog(ERROR, "cannot perform logical decoding without a acquired slot");
+		elog(ERROR, "cannot perform logical decoding without an acquired slot");
 
 	/* make sure the passed slot is suitable, these are user facing errors */
 	if (slot->data.database == InvalidOid)
@@ -436,7 +436,7 @@ CreateDecodingContext(XLogRecPtr start_lsn,
 }
 
 /*
- * Returns true if an consistent initial decoding snapshot has been built.
+ * Returns true if a consistent initial decoding snapshot has been built.
  */
 bool
 DecodingContextReady(LogicalDecodingContext *ctx)

src/backend/replication/logical/logicalfuncs.c

@@ -53,7 +53,7 @@ typedef struct DecodingOutputState
 } DecodingOutputState;
 
 /*
- * Prepare for a output plugin write.
+ * Prepare for an output plugin write.
  */
 static void
 LogicalOutputPrepareWrite(LogicalDecodingContext *ctx, XLogRecPtr lsn, TransactionId xid,

src/backend/replication/logical/reorderbuffer.c

@@ -286,7 +286,7 @@ ReorderBufferFree(ReorderBuffer *rb)
 }
 
 /*
- * Get a unused, possibly preallocated, ReorderBufferTXN.
+ * Get an unused, possibly preallocated, ReorderBufferTXN.
  */
 static ReorderBufferTXN *
 ReorderBufferGetTXN(ReorderBuffer *rb)
@@ -361,7 +361,7 @@ ReorderBufferReturnTXN(ReorderBuffer *rb, ReorderBufferTXN *txn)
 }
 
 /*
- * Get a unused, possibly preallocated, ReorderBufferChange.
+ * Get an unused, possibly preallocated, ReorderBufferChange.
  */
 ReorderBufferChange *
 ReorderBufferGetChange(ReorderBuffer *rb)
@@ -444,7 +444,7 @@ ReorderBufferReturnChange(ReorderBuffer *rb, ReorderBufferChange *change)
 
 
 /*
- * Get a unused, possibly preallocated, ReorderBufferTupleBuf
+ * Get an unused, possibly preallocated, ReorderBufferTupleBuf
  */
 ReorderBufferTupleBuf *
 ReorderBufferGetTupleBuf(ReorderBuffer *rb)
@@ -1531,7 +1531,7 @@ ReorderBufferCommit(ReorderBuffer *rb, TransactionId xid,
 		}
 
 		/*
-		 * There's a a speculative insertion remaining, just clean in up, it
+		 * There's a speculative insertion remaining, just clean in up, it
 		 * can't have been successful, otherwise we'd gotten a confirmation
 		 * record.
 		 */

src/backend/replication/logical/snapbuild.c

@@ -79,7 +79,7 @@
  *	  +--->|SNAPBUILD_CONSISTENT	 |<------------+
  *		   +-------------------------+
  *
- * Initially the machinery is in the START stage. When a xl_running_xacts
+ * Initially the machinery is in the START stage. When an xl_running_xacts
  * record is read that is sufficiently new (above the safe xmin horizon),
  * there's a state transition. If there were no running xacts when the
  * runnign_xacts record was generated, we'll directly go into CONSISTENT
@@ -161,7 +161,7 @@ struct SnapBuild
 
 	/*
 	 * Don't start decoding WAL until the "xl_running_xacts" information
-	 * indicates there are no running xids with a xid smaller than this.
+	 * indicates there are no running xids with an xid smaller than this.
 	 */
 	TransactionId initial_xmin_horizon;
 
@@ -683,8 +683,9 @@ SnapBuildProcessChange(SnapBuild *builder, TransactionId xid, XLogRecPtr lsn)
 }
 
 /*
- * Do CommandId/ComboCid handling after reading a xl_heap_new_cid record. This
- * implies that a transaction has done some form of write to system catalogs.
+ * Do CommandId/ComboCid handling after reading an xl_heap_new_cid record.
+ * This implies that a transaction has done some form of write to system
+ * catalogs.
  */
 void
 SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,

src/backend/replication/slot.c

@@ -437,7 +437,7 @@ ReplicationSlotDropAcquired(void)
 	/*
 	 * Rename the slot directory on disk, so that we'll no longer recognize
 	 * this as a valid slot.  Note that if this fails, we've got to mark the
-	 * slot inactive before bailing out.  If we're dropping a ephemeral slot,
+	 * slot inactive before bailing out.  If we're dropping an ephemeral slot,
 	 * we better never fail hard as the caller won't expect the slot to
 	 * survive and this might get called during error handling.
 	 */
@@ -546,7 +546,7 @@ ReplicationSlotMarkDirty(void)
 
 /*
  * Convert a slot that's marked as RS_EPHEMERAL to a RS_PERSISTENT slot,
- * guaranteeing it will be there after a eventual crash.
+ * guaranteeing it will be there after an eventual crash.
  */
 void
 ReplicationSlotPersist(void)