`dapp testnet` does not exit `geth` gracefully

@mbrock something I noticed using `dapp testnet --save x --load x`... you have a
```
( set -x; kill -INT $gethpid; wait )
```
inside `trap` to cleanly send a kill signal to geth so that it exits correctly. But it's not really working. When stopping `dapp testnet --save x --load x` geth often does not write blocks and when you load you end up with an older blockchain. I've done some tests and noticed that:
```
geth \
2> >(tee "$chaindir/geth.log" | grep --line-buffered Success | sed 's/^/geth: /' >&2) \
--datadir "$chaindir" --networkid "$CHAINID" --port="$port" \
--mine --minerthreads=1 \
--rpc --rpcapi "web3,eth,net,debug" --rpccorsdomain '*' --nodiscover \
--rpcport="$RPC_PORT" --unlock="$(IFS=,; echo "${address[*]}")" --password=<(exit) &
```
If I remove this line ` 2> >(tee "$chaindir/geth.log" | grep --line-buffered Success | sed 's/^/geth: /' >&2) \` then when I Ctrl + C, or `kill -INT $(pidof geth)` it exits gracefully and fully writes the blocks to disk.

I have no idea why redirecting the output from `geth` makes it not exit gracefully. Maybe it's something else I'm missing.