*sh: update sandbox aliases and functions

Having worked with various permutations of SSH and Mosh over the last
few days I've settled on the following:

  - use ControlMaster and friends in my ~/.ssh/config (I had turned it
    off when I first started experimenting with Mosh as it was getting
    in the way a little bit)
  - by default, use SSH to connect to sandbox (and specifically, the
    sandbox-clipper alias, which sets up reverse port forwarding and
    bails if forwarding fails); ie. `s sandbox-clipper` or just `s`
  - if port forwarding fails, use `k` alias (mnemonic: kill) to kill a
    stale connection that refuses to relinquish the port and then
    reconnect
  - when on a high-latency, unreliable link, use Mosh instead (note that
    SSH is much faster, still, on a low-latency, reliable link with a
    large screen area to redraw); this means using the `f` alias
    (mnemonic: forward) to set up a forwarding connection, and then `m`
    to connect with Mosh (an initial `k` might be needed if there is a
    lingering SSH connection getting in the way)

I wish it could be simpler, but with the current technology available,
this is the best I can do.

Signed-off-by: Wincent Colaiuta <win@wincent.com>