perf browser: Don't show scripts menu for 'perf top'

perf browser: Don't show scripts menu for 'perf top'

As 'perf top' has no data files to run scripts against. Also add a
is_report_browser() helper function to judge whether the running browser
is for 'perf report'.

Signed-off-by: Feng Tang <feng.tang@intel.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1351699257-5102-1-git-send-email-feng.tang@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>