unwind: determine shared libs from /proc/PID/maps

Until now, elfutils used dynamic loader internal structure to find the
shared libraries needed for unwinding and symbol resolution. This
structure was sometimes damaged and it seems that getting this info from
the maps file is more reliable in some other cases as well (vdso).

Related #127.

Signed-off-by: Martin Milata <mmilata@redhat.com>
Merge pull request #165 from abrt/gh127_report_maps

unwind: determine shared libs from /proc/PID/maps