remove setting tty to raw when linking

this appears to be flaky, and is only really a UX thing where the 99% case is
not user-interfacing.

:(
make sure trap is registered before stopping

Signed-off-by: Sheel Choksi <sheelc@pivotallabs.com>
don't exercise flaky tty code path in test

this is a hard one. sometimes nothing shows up on the command's stdin, at all.
seems to happen regardless of iodaemon/etc.

Signed-off-by: Sheel Choksi <sheelc@pivotallabs.com>