dead-end forks identification at github and bitbucket repositories

Related to: https://github.com/golang/gddo/issues/126

Rules for dead-end forks:
- github: https://github.com/mcuadros/gddo/blob/endfork/gosrc/github.go#L160
- bitbucket: https://github.com/mcuadros/gddo/blob/endfork/gosrc/bitbucket.go#L54, at bitbutcket we check that is a fork, because in bitbucket created and updated are always related to the fork.

In the package page I added the label `(dead-end fork)`
![screen shot 2014-10-04 at 17 03 37](https://cloud.githubusercontent.com/assets/1573114/4515894/a866ac40-4bd7-11e4-92cc-345e72ab6cb5.png)