* exceptions.cc (stack_info::walk): Use method to find offset.

* exceptions.cc (stack_info::walk): Use method to find offset.
(handle_exceptions): Be more assertive in finding ebp for use under W2K.
Create a dummy stack frame for cases where program is dying and a stack dump is
being output.
(sig_handle): Fill out a GetThreadContext for use with a user-generated "core
dump".