Fixed server.restart function called twice #1

* fixed callback called propery
* useless test code removed
changed server.listen error message
Fixed debug message in the restarted callback #1
timeout object cleared properly in `sever.listen` function #1
callback called properly when `options.delay=0`
add test `options.delay=0`
Merge pull request #2 from narirou/dev

Fixed server.restart function called twice