Reflect git changes at root level

[glangford]

Beginner fix for #564. This change seems to work in interactive testing, but apm test reports one failure. I don't know how to rectify this. Any suggestions?

 TreeView
  Git status decorations
    when the project is a symbolic link to the repository root
      when a file loses its modified status
        it updates its and its parent directories' styles

[glangford]

I started this looking at tree-view, but perhaps a better fix than #614 is to start at the level of the GitRepository class in atom; getDirectoryStatus appears to turn a path at root level into just "/". So getDirectoryStatus always returns a status of zero for the root.

getDirectoryStatus: (directoryPath)  ->
    directoryPath = "#{@relativize(directoryPath)}/"  #############
    directoryStatus = 0
    for path, status of @statuses
      directoryStatus |= status if path.indexOf(directoryPath) is 0
    directoryStatus

https://github.com/atom/atom/blob/master/src/git-repository.coffee#L305

[winstliu]

Superseded by #1144.