Now stores last values and returns ruby object.
Delete files and dirs after tests
Removed calls to #ruby_object and #exit_status
Use PTY instead of IO.popen

Wasn't getting stdout to print.
Attempt to fix mixing of builtins with ruby code
Use $PROMPT if it's set
Converted RemoteShell to return actual ruby objects instead of CommandResults

Also tidied up LocalShell en lieu of making the two shells consistent.
PTY tests should've stubbed readpartial