"oldshell" command should use `OldShell` on failure instead of `Shell`
"oldshell" command should use `OldShell` on failure instead of `Shell`

following up https://github.com/sbt/sbt/pull/3098

sbt/sbt,sbt/sbt,sbt/sbt,sbt/sbt,sbt/sbt,sbt/sbt,sbt/sbt