Add --show-nr-samples option to "perf annotate" so that it matches "perf
report".

Committer note:

Note that it can't be used together with --show-total-period, which
seems like a silly limitation, that can be lifted at some point.

Made it bail out if not on --stdio.
Signed-off-by: Taeung Song <treeze.taeung@gmail.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Milian Wolff <milian.wolff@kdab.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: http://lkml.kernel.org/r/1503046008-5511-1-git-send-email-treeze.taeung@gmail.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>