Better handling of infinite recursion

unwind: Append threads/frames in O(1)
unwind: throw away the most recent frames
unwind: lower stacktrace length limit to 256

Fixes #179.

Signed-off-by: Martin Milata <mmilata@redhat.com>
Include git commit in non-release version

I don't like it very much but at least we'll be consistent with other
ABRT projects.

jfilak:
I back ported this patch from master because of the same troubles with
the ABRT integration tests as described in #184.

Signed-off-by: Jakub Filak <jfilak@redhat.com>

Conflicts:
	autogen.sh
	configure.ac