Found a bug in LTM 0.39 (line 83 of ...

Found a bug in LTM 0.39 (line 83 of bn_fast_s_mp_mul_high_digs.c) thanks to Valgrind. I will do a quicky release of LTM 0.40 on Friday along with LTC 1.15 (found a Yarrow bug with Valgrind as well… w00t)