perf tui: Allow disabling the TUI on a per command basis in ~/.perfconfig

Using the same scheme as for git's/perf's pager setup, i.e. if one
doesn't want to, on a newt enabled perf binary, to disable the TUI for
'perf report', its just a matter of doing:

  [root@doppio linux-2.6-tip]# printf "[tui]\n\nreport = off\n" >
  /root/.perfconfig
  [root@doppio linux-2.6-tip]# cat /root/.perfconfig
  [tui]

  report = off
  [root@doppio linux-2.6-tip]#

System wide settings are also possible, by editing /etc/perfconfig, etc,
i.e. the git machinery for config files applies to perf as well, so when
in doubt where to put your settings, consult the git documentation, if
it fails, please let us know.

Suggested-by: Ingo Molnar <mingo@elte.hu>
Discussed-with: Stephane Eranian <eranian@google.com>
Cc: Frédéric Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Stephane Eranian <eranian@google.com>
Cc: Tom Zanussi <tzanussi@gmail.com>
LKML-Reference: <new-submission>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>