Local project source in Godeps

Adds the ability to specify local source directories in the Godeps file. 

The source can either be a relative path to a source directory or an absolute path on the file system

```
myrepo.com/my/project .
myrepo.com/my/awesomeProject ../awesomeProject
myrepo.com/my/otherProject /path/to/my/otherProject
```