More improvements to `mlv_play`
Created originally on Bitbucket by ayshih (Albert Shih)
Was already merged in Bitbucket before import, marked as merged by the import user
Added another change to an existing PR
- Fixes the bug pointed out in commit d6868651c828 (part of pull request 555) where exact playback of RAW videos wasn't working when frames needed to be skipped, which was because the read pointer wasn't actually advanced.
- FIO_SeekSkipFile_emulate wasn't working properly, at least on the 50D, when crossing the 2GB boundary (because the underlying FIO_SeekFile doesn't work well with signed/unsigned 32-bit integers). Converted everything to FIO_SeekSkipFile (and fixed a bug associated with that), but this will break compilation on models that haven't yet found that stub.