Fixed inconsistent txs returned from listtransactions

listtransactions had a weird behaviour.

Having a couple of send/receive txs on my wallet, I ended up with 29 txs in total.
Funny thing is, if I called listtransactions with tx_count and from_tx parameters respectively 100, 0, I got this:
```
>>> len(armory_conn.listtransactions(100, 0))
33
```
Now, calling it with from_tx 30:
```
>>> len(armory_conn.listtransactions(100, 30))
0
```
and so on...
```
>>> len(armory_conn.listtransactions(100, 28))
2
>>> len(armory_conn.listtransactions(100, 27))
4
>>> len(armory_conn.listtransactions(100, 26))
6
>>> len(armory_conn.listtransactions(100, 25))
7
>>> len(armory_conn.listtransactions(100, 24))
9
```

I found out that *send* txs were added twice. (https://github.com/etotheipi/BitcoinArmory/blob/0.91-dev/armoryd.py#L533)
```
  # We always add one entry for the total balance diff on outgoing tx
```
I don't really know why this is needed, but that is not good for me, since it messes up with the tx offset (from_tx parameter)

Hope it helps!