include_original=False can exclude user-specified representation #132

If one of the representations specified in auto_generate_representations matches the original, include_original=False causes it to be skipped

To Reproduce
Steps to reproduce the behavior:

1. Let's say we have a 1920x1080 video
2. Transcode the video using hls.auto_generate_representations([1080, 480, 240], include_original=False)
3. The playlist will contain 854x480 and 426x240, but not 1920x1080

Expected behavior
The playlist should contain all representations that are explicitly provided by the user (in the example above: 1080, 480, 240).