enabled copying of symlinked dirs; updated tests

[chrisekelley]

2 lines of code called directly lstat, instead of using the local stat
function, which tests if dereference == true

[chrisekelley]

There is still a failed test - "mirror regular fs to custom fs" in test/index.js line 135:

    operator: error
    expected: |-
      undefined
    actual: |-
      { [Error: EISDIR: illegal operation on a directory, read] errno: -21, code: 'EISDIR', syscall: 'read' }
    at: EventEmitter.<anonymous> (/Users/ckelley/source/mirror-folder/test/index.js:135:9)
    stack: |-
      Error: EISDIR: illegal operation on a directory, read

I wonder if it is not catching the "dereference:true" property?

    var progress = mirror(fixtures, {fs: archive, name: '/', dereference: true}, function (err) {

[chrisekelley]

If you accept this PR, I'd recommend updating the README to be very clear that if you have symlinks, you will get an error unless you set dereference:true.