Unify unwind_block and unwind_except_handler
Unify unwind_block and unwind_except_handler

The latter is a special case of the former.

sukwon0709/byterun,sukwon0709/byterun,kostyll/byterun,sukwon0709/byterun,nedbat/byterun,sukwon0709/byterun,sukwon0709/byterun,djhenderson/byterun