Make some spelling more consistent

src/backend/commands/typecmds.c

@@ -929,7 +929,7 @@ DefineDomain(CreateDomainStmt *stmt)
 				if (constr->is_no_inherit)
 					ereport(ERROR,
 							(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
-							 errmsg("CHECK constraints for domains cannot be marked NO INHERIT")));
+							 errmsg("check constraints for domains cannot be marked NO INHERIT")));
 				break;
 
 				/*

src/backend/parser/parse_agg.c

@@ -248,7 +248,7 @@ transformAggregateCall(ParseState *pstate, Aggref *agg,
 			break;
 		case EXPR_KIND_CHECK_CONSTRAINT:
 		case EXPR_KIND_DOMAIN_CHECK:
-			err = _("aggregate functions are not allowed in CHECK constraints");
+			err = _("aggregate functions are not allowed in check constraints");
 			break;
 		case EXPR_KIND_COLUMN_DEFAULT:
 		case EXPR_KIND_FUNCTION_DEFAULT:
@@ -516,7 +516,7 @@ transformWindowFuncCall(ParseState *pstate, WindowFunc *wfunc,
 			break;
 		case EXPR_KIND_CHECK_CONSTRAINT:
 		case EXPR_KIND_DOMAIN_CHECK:
-			err = _("window functions are not allowed in CHECK constraints");
+			err = _("window functions are not allowed in check constraints");
 			break;
 		case EXPR_KIND_COLUMN_DEFAULT:
 		case EXPR_KIND_FUNCTION_DEFAULT:

src/backend/parser/parse_expr.c

@@ -1449,7 +1449,7 @@ transformSubLink(ParseState *pstate, SubLink *sublink)
 			break;
 		case EXPR_KIND_CHECK_CONSTRAINT:
 		case EXPR_KIND_DOMAIN_CHECK:
-			err = _("cannot use subquery in CHECK constraint");
+			err = _("cannot use subquery in check constraint");
 			break;
 		case EXPR_KIND_COLUMN_DEFAULT:
 		case EXPR_KIND_FUNCTION_DEFAULT:

src/backend/utils/adt/rangetypes.c

@@ -393,7 +393,7 @@ range_constructor3(PG_FUNCTION_ARGS)
 	if (PG_ARGISNULL(2))
 		ereport(ERROR,
 				(errcode(ERRCODE_DATA_EXCEPTION),
-			   errmsg("range constructor flags argument must not be NULL")));
+			   errmsg("range constructor flags argument must not be null")));
 
 	flags = range_parse_flags(text_to_cstring(PG_GETARG_TEXT_P(2)));