Combined improvement of shell scripts
    
    - quote arrays/variables to avoid globbing/splitting
    - exit on failed cd calls
    - group file directs for consecutive command outputs
    - define default exit values and set exit value explicitly for
      tests which succeed
    - comment vim modeline instructions
    - use uniform quoting style
    - use uniform indentation
    
    This makes ShellCheck pass with no errors/warnings.
    
    Signed-off-by: Georg Pfuetzenreuter <mail@georg-pfuetzenreuter.net>