Under some circumstances, newSVpv() returns SV of higher type than
SVt_PVIV, such as SVt_PVMG.

Lubomir Rintel <lkundrak@v3.sk>
Upstream: http://repo.or.cz/w/Text-CSV_XS.git?a=commit;h=72d4bab14e22e62699e90eeb306c606435ef31a6

diff -urp Text-CSV_XS-0.52.orig/CSV_XS.xs Text-CSV_XS-0.52/CSV_XS.xs
--- Text-CSV_XS-0.52.orig/CSV_XS.xs	2008-06-17 12:20:00.000000000 +0200
+++ Text-CSV_XS-0.52/CSV_XS.xs	2008-07-08 14:42:33.000000000 +0200
@@ -181,7 +181,7 @@ static SV *SetDiag (csv_t *csv, int xse)
 
     while (xs_errors[i].xs_errno && xs_errors[i].xs_errno != xse) i++;
     if ((err = newSVpv (xs_errors[i].xs_errstr, 0))) {
-	sv_upgrade (err, SVt_PVIV);
+	SvUPGRADE (err, SVt_PVIV);
 	SvIV_set (err, xse);
 	SvIOK_on (err);
 	hv_store (csv->self, "_ERROR_DIAG",  11, err,           0);