Lumo shouldn't crash if it can't bind to socket REPL port

[anmonteiro]

Lumo socket REPL listening at localhost:555.
cljs.user=> events.js:163
      throw er; // Unhandled 'error' event
      ^

Error: listen EACCES 127.0.0.1:555
    at Object.exports._errnoException (util.js:1050:11)
    at exports._exceptionWithHostPort (util.js:1073:20)
    at Server.setupListenHandle [as _listen2] (net.js:1247:19)
    at listenInCluster (net.js:1304:12)
    at doListen (net.js:1428:7)
    at GetAddrInfoReqWrap.asyncCallback [as callback] (dns.js:62:16)
    at GetAddrInfoReqWrap.onlookup [as oncomplete] (dns.js:78:10)