Add extension free function.

(Imported from upstream's 984a30423d70126ed1df30e4b52962398cdaa9b6.)
diff --git a/crypto/x509v3/v3_lib.c b/crypto/x509v3/v3_lib.c
index b921499..0119b45 100644
--- a/crypto/x509v3/v3_lib.c
+++ b/crypto/x509v3/v3_lib.c
@@ -120,6 +120,27 @@
 	return X509V3_EXT_get_nid(nid);
 }
 
+int X509V3_EXT_free(int nid, void *ext_data)
+{
+	    const X509V3_EXT_METHOD *ext_method = X509V3_EXT_get_nid(nid);
+	    if (ext_method == NULL)
+	    {
+		    OPENSSL_PUT_ERROR(X509V3, X509V3_EXT_free, X509V3_R_CANNOT_FIND_FREE_FUNCTION);
+		    return 0;
+	    }
+
+	    if (ext_method->it != NULL)
+		    ASN1_item_free(ext_data, ASN1_ITEM_ptr(ext_method->it));
+	    else if (ext_method->ext_free != NULL)
+		    ext_method->ext_free(ext_data);
+	    else
+	    {
+		    OPENSSL_PUT_ERROR(X509V3, X509V3_EXT_free, X509V3_R_CANNOT_FIND_FREE_FUNCTION);
+		    return 0;
+	    }
+
+	    return 1;
+}
 
 int X509V3_EXT_add_list(X509V3_EXT_METHOD *extlist)
 {