a-a-a-vmcore: save kernel version in 'kernel' file

Related to rhbz#921949

Signed-off-by: Jakub Filak <jfilak@redhat.com>
Signed-off-by: Martin Milata <mmilata@redhat.com>
a-a-g-core-backtrace: don't crash if kernel file doesn't exist

Closes rhbz#921949

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