gdb: quality frame has to have file name

With MiniDebugInfo, almost every frame has function_name present - but
we want more. With full debuginfo we also get file name and line number.
The file name has to be present now in order to count the frame as good
in stacktrace quality computation.

Closes abrt/abrt#851.
Related to rhbz#1149431.

Signed-off-by: Martin Milata <mmilata@redhat.com>
Merge pull request #188 from abrt/gh851_backtrace_quality

gdb: quality frame has to have file name