Running "perf top" on a machine with possibly invalid or non-matching
vmlinux at the various places results in no symbol resolving despite
/proc/kallsyms being present and valid.

Add a new option --ignore-vmlinux to explicitly indicate that we do not
want to use these kernels and just use what we have (kallsyms).
Signed-off-by: NWilly Tarreau <w@1wt.eu>
Cc: Ingo Molnar <mingo@redhat.com>
Link: http://lkml.kernel.org/r/20130914083259.GA3418@1wt.euSigned-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>