function isWrapped(cmd) {
  return cmd.endsWith(')');
}
Returns true if the node repl has passed in the command with extra
paren-wrapping added. The reason this works is because in the unwrapped
case, |cmd| always ends with a newline.

Needless to say, this code will break if someone decides to randomly add
whitespace to that part of node's lib/repl.js -- but that seems unlikely.
More likely is that the whole interface changes, which means everything
has to be rewritten anyway.
@param cmd The command passed to the custom eval function.