Correct unwind region length calculations.

Correct unwind region length calculations.
	* config/tc-ia64.c (struct unw_rec_list): Add slot_frag field.
	(struct unwind): Add next_slot_frag field.
	(slot_index): New parameters slot_frag and first_frag.  Add code
	to add in frag sizes when different.  Add comments.
	(fixup_unw_records): New locals first_frag and last_frag.  Pass new
	arguments to slot_index.
	(emit_one_bundle): Set slot_frag field.  Set next_slot_number after
	loop end.  Set next_slot_frag field.