Abort XHRs after 45s and trigger an error
Playlist and segment requests will now abort. Segment requests should continue to be retried automatically. Playlist requests will trigger a MEDIA_ERR_NETWORK.
Rename variable

`abortTimeout` is a little less overloaded than `timeout`.
Merge pull request #78 from videojs/feature/xhr-timeouts

Abort XHRs after 45s and trigger an error