The current -z option does almost nothing.  It doesn't zero the existing
samples so that we can see profiles of exited process after last
refresh.  It seems it only affects annotation.

This patch clears existing entries before processing if -z option is
given.  For this original decaying logic also moved before processing.
Reported-by: NStephane Eranian <eranian@google.com>
Tested-by: NStephane Eranian <eranian@google.com>
Signed-off-by: NNamhyung Kim <namhyung@kernel.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung.kim@lge.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/1407831366-28892-1-git-send-email-namhyung@kernel.orgSigned-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>