perf tools: Compare hists comm by addresses

Now that comm strings are allocated only once and refcounted to be shared
among threads, these can now be safely compared by addresses. This
should remove most hists collapses on post processing.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Tested-by: Jiri Olsa <jolsa@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/1381468543-25334-8-git-send-email-namhyung@kernel.org


Signed-off-by: Namhyung Kim <namhyung@kernel.org>