Wait 1s before autobuild util there is no file change.

Change the way to detect duplicated build.

BTW, when developing directory is located in a network filesystem such as NFS, because of operation delay, bee run might report below error message:

```
2014/11/25 00:38:10 [app.go:96] [I] http server Running on :8080
routers/router.go:6:2: 
controllers/internal.go:1:1: expected 'package', found 'EOF'
2014/11/25 00:38:10 [ERRO] ============== Build failed ===================
```

Waiting for 1s before autobuild is enough for most situation.