Improve --list to show current exist probes with line number and
file name. This enables user easily to check which line is
already probed.

for example:

 ./perf probe --list
 probe:vfs_read       (on vfs_read:8@linux-2.6-tip/fs/read_write.c)
Signed-off-by: Masami Hiramatsu <mhiramat@redhat.com>
Cc: systemtap <systemtap@sources.redhat.com>
Cc: DLE <dle-develop@lists.sourceforge.net>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20100316220619.32050.48702.stgit@localhost6.localdomain6>
Signed-off-by: Ingo Molnar <mingo@elte.hu>