perf top: Use address pattern in lookup_sym_source

Because we may have aliases, like __GI___strcoll_l in
/lib64/libc-2.10.2.so that appears in objdump as:

$ objdump --start-address=0x0000003715a86420 \
           --stop-address=0x0000003715a872dc -dS /lib64/libc-2.10.2.so

0000003715a86420 <__strcoll_l>:
  3715a86420:	55                   	push   %rbp
  3715a86421:	48 89 e5             	mov    %rsp,%rbp
  3715a86424:	41 57                	push   %r15
[root@doppio linux-2.6-tip]#

So look for the address exactly at the start of the line instead
so that annotation can work for in these cases.

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frédéric Weisbecker <fweisbec@gmail.com>
Cc: Kirill Smelkov <kirr@landau.phys.spbu.ru>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
LKML-Reference: <1265550376-12665-2-git-send-email-acme@infradead.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>