perf ui/stdio: Align column header for hierarchy output

The hierarchy output mode is to group entries so the existing columns
won't fit to the new output.  Treat all sort keys as a single column and
separate headers by "/".

  #    Overhead  Command / Shared Object
  # ...........  ................................
  #
      15.11%     swapper
         14.97%     [kernel.vmlinux]
          0.09%     [libahci]
          0.05%     [iwlwifi]
  ...

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Pekka Enberg <penberg@kernel.org>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/r/1456326830-30456-11-git-send-email-namhyung@kernel.org


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>