* exceptions.cc (stack_info): Add some controls.

* exceptions.cc (stack_info): Add some controls.
(stack_info::init): Add extra arguments to control method of initialization..
If we have a known good frame, set things up so that this frame is not skipped
the first time through.  Record whether caller cares about arguments or not.
(stack_info::walk): Don't store arguments if they're unwanted.
(stackdump): Add isexception parameter for use when called by exception
handler.
(cygwin_stackdump): Accomodate extra argument to stackdump.
(handle_exceptions): Ditto.
(sig_handle): Ditto.
(interrupt_on_return): Accomodate extra arguments to stack walk initialization.