Use path.sep

[MichaReiser]

In multiple places '/' is used to check if it is a directory or is appended when missing at the end.

e.g. the following code from libaries.load.

  if (root && !/\/$/.test(root)) {
    root = root + '/';
  }

Instead path.sep should be used to be cross platform compatible.

Maybe a better approach would be to always use / internaly and only call path.normalize when the file or directory should be accessed. This would avoid all the special handling in all the plugins and core code for different path seperators.