poptoshell: Initial stab at workaround for tramp "Args out of range"

poptoshell: Initial stab at workaround for tramp "Args out of range"

More than occasionally, tramp fails to reconnect to shells that were
disconnected gracelessly, with "byte-code: Args out of range:
...". Using tramp-cleanup-this-connection then retrying often works, so
let's do that.

It's hard to test this easily, so I'm checking in a preliminary version
to tweak incrementally.