will_abort: configurable crash-time stack

There's 26 functions that call each other. You can either run

  will_abort --random

to get random stack, or

  will_abort lowercasestring

to get a stack that is determined by the string argument.
The implementation is kinda retarded but it seems to work.

Signed-off-by: Martin Milata <mmilata@redhat.com>
Merge pull request #5 from mmilata/configurable_stack

will_abort: configurable crash-time stack