pass a string with embedded quotes, perl hands it off to a shell which
results in an extra shell wrapper for every ssh. Well, with SSH_ARGS
the way they are, that means we always get the extra shell. While this
is a nice optimization it actually matters mostly from
linktest_control where I want to make sure that the child that invokes
linktest on ops (an ssh) can be killed directly with TERM (say, if
user cancels linktest) without worrying about intervening shell
screwing with signals, etc.