The '--call-graph' command line option can receive undocumented optional
print_limit argument. Besides, use strtoul() to parse the option since
its type is u32.

Cc: Ingo Molnar <mingo@elte.hu>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1323703017-6060-2-git-send-email-namhyung@gmail.comSigned-off-by: NNamhyung Kim <namhyung@gmail.com>
Signed-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>