Issue when src and dest is the same path

Hi, thanks for your great plugin, it very helpful!

I notice small issue: it seems to doesn't work when task configured the way when source and destination is the same file.

Example:

    concat: {
      banner: {
        options: {
          banner: "some banner ..."
        },
        expand: true,
        flatten: false,
        cwd: 'dist',
        src: '*.js',
        dest: 'dist'
      }
    }

I use `grunt-contrib-concat` to add banners (I know it not very smart, but works). When I try to run `concat` task, configured like this, through `newer` it always handle zero files.

P.S.
Sory for my bad english.