perf symbols: Improve debugging information about symtab origins

Be more clear about DSO long names and tell from which file
kernel symbols were obtained, all in --verbose mode:

    [root@mica ~]# perf report -v > /dev/null
    Looking at the vmlinux_path (5 entries long)
    Using /lib/modules/2.6.33-rc8-tip-00777-g0918527-dirty/build/vmlinux for symbols
    [root@mica ~]# mv /lib/modules/2.6.33-rc8-tip-00777-g0918527-dirty/build/vmlinux /tmp/dd
    [root@mica ~]# perf report -v > /dev/null
    Looking at the vmlinux_path (5 entries long)
    Using /proc/kallsyms for symbols
    [root@mica ~]#

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frédéric 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: <1266866139-6361-1-git-send-email-acme@infradead.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>