unwind: Port to current API of elfutils unwinder

Related to rhbz#1051569.

Signed-off-by: Martin Milata <mmilata@redhat.com>
Merge pull request #150 from abrt/rhbz1051569-elfutils

unwind: Port to current API of elfutils unwinder

Related to rhbz#1051569.

Signed-off-by: Martin Milata <mmilata@redhat.com>