add missing declaration

Submitted by: Nils Larsch

crypto/bn/bn_lcl.h

diff --git a/crypto/bn/bn_lcl.h b/crypto/bn/bn_lcl.h
index 73792f1..8a4dba3 100644
--- a/crypto/bn/bn_lcl.h
+++ b/crypto/bn/bn_lcl.h
@@ -428,6 +428,8 @@
 	BN_ULONG *t);
 void bn_mul_high(BN_ULONG *r,BN_ULONG *a,BN_ULONG *b,BN_ULONG *l,int n2,
 	BN_ULONG *t);
+BN_ULONG bn_add_part_words(BN_ULONG *r, const BN_ULONG *a, const BN_ULONG *b,
+	int cl, int dl);
 BN_ULONG bn_sub_part_words(BN_ULONG *r, const BN_ULONG *a, const BN_ULONG *b,
 	int cl, int dl);