perf diff: Fix usage array, it must end with a NULL entry

Fixing this:

 [acme@doppio linux-2.6-tip]$ perf diff --hell
   Error: unknown option `hell'

  usage: perf diff [<options>] [old_file] [new_file]
 Segmentation fault
 [acme@doppio linux-2.6-tip]$

Also go over the other such arrays to check if they all were OK,
they are, but there were some minor changes to do like making
one static and renaming another to match the command it refers
to.

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
LKML-Reference: <1261161358-23959-1-git-send-email-acme@infradead.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>