preserve stty settings

 * saves and restores stty settings instead of overwriting them with
   sane

I think this should fix the problems discussed in https://github.com/trptcolin/reply/issues/117

Before this patch

    java -cp target/jline-2.12-SNAPSHOT.jar:target/jline-2.12-SNAPSHOT-tests.jar jline.example.Example

would mutate the settings of `stty` and after this patch it does not.