Feature port auto retry

[Mzack9999]

No description provided.

[ehsandeep]

Auto retry is not working, if another HTTP service is listening on 8000, simplehttpserver just start on the same port and does receive any incoming request.

$./simplehttpserver -v
Serving . on http://0.0.0.0:8000/...

[Mzack9999]

On Windows and OSX listening on the same port is allowed as binaries are compiled with SO_REUSEPORT flag. On linux it isn't, so it behaves as expected:

$ go run .
Serving . on http://0.0.0.0:8000/...
Can't listen on 0.0.0.0:8000: listen tcp 0.0.0.0:8000: bind: address already in use - retrying with another port
Serving . on http://0.0.0.0:8001/...
Can't listen on 0.0.0.0:8001: listen tcp 0.0.0.0:8001: bind: address already in use - retrying with another port
Serving . on http://0.0.0.0:8002/...