Set 'NA' as the default value for missing fields in the output template (fixes #1931)

Remove the `except KeyError` clause, it won't get raised anymore
[YoutubeDL] Simplify filename preparation
[soundcloud] Do not mistake original_format for ext (Fixes #1934)
[zdf] Correct order of unknown formats (#1936)
release 2013.12.10
[mtv] Fixup incorrectly encoded XML documents
[soundcloud] Fix the extension for 'downloadable' songs

In this case the 'original_format' field must be used.
[mixcloud] Try to get the m4a url if the mp3 url fails to download (fixes #1939)
add MDRIE
[dailymotion] Fix uploader extraction

Now it looks directly in the info dictionary
[dailymotion] Fix view count extraction and make it non fatal (fixes #1940)
[vimeo] Fix the extraction for some 'player' or 'pro' videos

The variable the config dict is assigned to can change, now we try to detect it or fallback to a, b or c
[vimeo] Fix unused argument of the `_real_extract` method
Use `_download_xml` in more extractors
release 2013.12.11
Fix thumbnail filename determination (Fixes #1945)
release 2013.12.11.1
[pornhub] Fix URL regexp
release 2013.12.11.2
[channel9] Initial implementation (#1885)