add crash-type-agnostic optimized thread generators

[jfilak]

The functions should work as sr_gdb_stacktrace_get_optimized_thread() Optimized stacktraces are used by bugzilla reporter when an original backtrace is too big to be added to comment 0.

[jfilak]

btparser generates an optimized thread in the following format for CCpp:

Thread no. 1 (10 frames)
 #4 gtk_list_store_compare_func at gtkliststore.c:1961
 #5 node_find_closest at gsequence.c:1764
 #6 node_insert_sorted at gsequence.c:2002
 #7 g_sequence_sort_changed_iter at gsequence.c:961
 #8 gtk_list_store_insert_with_valuesv at gtkliststore.c:2327
 #9 ffi_call_unix64 at ../src/x86/unix64.S:75
 #10 ffi_call at ../src/x86/ffi64.c:486
 #11 g_callable_info_invoke at girepository/gicallableinfo.c:610
 #12 g_function_info_invoke at girepository/gifunctioninfo.c:274
 #13 _invoke_callable at pygi-invoke.c:52

And I would expected that it is possible to generate a similar stacktrace for all crash types. It will make bugzilla reports clearer.

Python standard backtrace:

Traceback (most recent call last):
  File "/usr/lib64/python2.7/site-packages/gnome_abrt/views.py", line 405, in on_tvs_problems_changed
    selection = self._get_selected(selection)
  File "/usr/lib64/python2.7/site-packages/gnome_abrt/views.py", line 401, in _get_selected
    return [model[p][2] for p in rows]
  File "/usr/lib64/python2.7/site-packages/gi/overrides/Gtk.py", line 1043, in __getitem__
    return self.model.get_value(self.iter, key)
  File "/usr/lib64/python2.7/site-packages/gi/types.py", line 113, in function
    return info.invoke(*args, **kwargs)
ValueError: 2 not in range -2147483648 to 2147483647

Python optimized backtrace:

#0 function at /usr/lib64/python2.7/site-packages/gi/types.py": 113
#1 __getitem__ at /usr/lib64/python2.7/site-packages/gi/overrides/Gtk.py: 1043
#2 _get_selected at /usr/lib64/python2.7/site-packages/gnome_abrt/views.py: 401
#3 on_tvs_problems_changed at /usr/lib64/python2.7/site-packages/gnome_abrt/views.py: 405

[mmilata]

Implemented in 7ef55a0