Improve `run --dev` to use interactive debugger
Improve `run --dev` to use interactive debugger

Instead of simply exiting the `--dev` option now drops into an interactive post mortem debugger on unhandled exceptions.

gsalgado/pyethapp,changwu-tw/pyethapp,ethereum/pyethapp,ethereum/pyethapp,changwu-tw/pyethapp,RomanZacharia/pyethapp,RomanZacharia/pyethapp,gsalgado/pyethapp,d-das/pyethapp