Fix spelling errors and typos in comments

Author: Daniel Gustafsson <daniel@yesql.se>

src/backend/executor/execExprInterp.c

@@ -1622,7 +1622,7 @@ ExecInterpExpr(ExprState *state, ExprContext *econtext, bool *isnull)
 
 		/*
 		 * Evaluate aggregate transition / combine function that has a
-		 * by-value transition type. That's a seperate case from the
+		 * by-value transition type. That's a separate case from the
 		 * by-reference implementation because it's a bit simpler.
 		 */
 		EEO_CASE(EEOP_AGG_PLAIN_TRANS_BYVAL)

src/backend/executor/execPartition.c

@@ -852,7 +852,7 @@ ExecCleanupTupleRouting(ModifyTableState *mtstate,
 	{
 		ResultRelInfo *resultRelInfo = proute->partitions[i];
 
-		/* skip further processsing for uninitialized partitions */
+		/* skip further processing for uninitialized partitions */
 		if (resultRelInfo == NULL)
 			continue;