Minor spelling fixes

Fix a few spelling mistakes.

Per bug report #8193 from Lajos Veres.

Author: sfrost

contrib/pg_upgrade/relfilenode.c

@@ -258,7 +258,7 @@ transfer_relfile(pageCnvCtx *pageConverter, FileNameMap *map,
 				if (errno == ENOENT)
 					return;
 				else
-					pg_log(PG_FATAL, "error while checking for file existance \"%s.%s\" (\"%s\" to \"%s\"): %s\n",
+					pg_log(PG_FATAL, "error while checking for file existence \"%s.%s\" (\"%s\" to \"%s\"): %s\n",
 						   map->nspname, map->relname, old_file, new_file,
 						   getErrorText(errno));
 			}

src/backend/access/transam/xlogreader.c

@@ -903,7 +903,7 @@ ValidXLogPageHeader(XLogReaderState *state, XLogRecPtr recptr,
 /*
  * Find the first record with at an lsn >= RecPtr.
  *
- * Useful for checking wether RecPtr is a valid xlog address for reading and to
+ * Useful for checking whether RecPtr is a valid xlog address for reading and to
  * find the first valid address after some address when dumping records for
  * debugging purposes.
  */

src/backend/utils/adt/tsrank.c

@@ -530,11 +530,11 @@ typedef struct
 	int			q;
 	DocRepresentation *begin;
 	DocRepresentation *end;
-} Extention;
+} CoverExt;
 
 
 static bool
-Cover(DocRepresentation *doc, int len, QueryRepresentation *qr, Extention *ext)
+Cover(DocRepresentation *doc, int len, QueryRepresentation *qr, CoverExt *ext)
 {
 	DocRepresentation *ptr;
 	int			lastpos = ext->pos;
@@ -729,7 +729,7 @@ calc_rank_cd(float4 *arrdata, TSVector txt, TSQuery query, int method)
 	int			len,
 				i,
 				doclen = 0;
-	Extention	ext;
+	CoverExt	ext;
 	double		Wdoc = 0.0;
 	double		invws[lengthof(weights)];
 	double		SumDist = 0.0,
@@ -759,7 +759,7 @@ calc_rank_cd(float4 *arrdata, TSVector txt, TSQuery query, int method)
 		return 0.0;
 	}
 
-	MemSet(&ext, 0, sizeof(Extention));
+	MemSet(&ext, 0, sizeof(CoverExt));
 	while (Cover(doc, doclen, &qr, &ext))
 	{
 		double		Cpos = 0.0;

src/tools/pgindent/typedefs.list

@@ -326,6 +326,7 @@ CopyStmt
 Cost
 CostSelector
 Counters
+CoverExt
 CoverPos
 CreateCastStmt
 CreateConversionStmt
@@ -487,7 +488,6 @@ ExtensionBehavior
 ExtensionControlFile
 ExtensionInfo
 ExtensionVersionInfo
-Extention
 FDWCollateState
 FD_SET
 FILE