perf stat: Enhance option parse error message

Print related option help messages only when it failed to process
options.  While at it, modify parse_options_usage() to skip usage part
so that it can be used for showing multiple option help messages
naturally like below:

  $ perf stat -Bx, ls
  -B option not supported with -x

   usage: perf stat [<options>] [<command>]

      -B, --big-num         print large numbers with thousands' separators
      -x, --field-separator <separator>
                            print counts with custom separator

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Enthusiastically-Supported-by: Ingo Molnar <mingo@kernel.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1383291195-24386-6-git-send-email-namhyung@kernel.org


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