FIX: MsgSeqNum should be ignored in Sequence Reset (Reset mode)

As per FIX specification MsgSeqNum in the header should be
ignored in the Reset mode. Use incoming sequence number instead.

This should fix the issue #48

Reported-by: @Poordeveloper
Signed-off-by: Marat Stanichenko <mstanichenko@gmail.com>
Signed-off-by: Pekka Enberg <penberg@iki.fi>