Add %_multiartist% and fix default renaming.

See http://forums.musicbrainz.org/viewtopic.php?pid=25318
Remove debug print statement
Add NEWS.
Use getall rather than split by ; (bitmap)
Handle NAT tracks with feat. artists.

Add %_primaryartist% and %_primaryartistsort% and use
%_primaryartist% in default naming string.
Revert "Handle NAT tracks with feat. artists."

This reverts commit 0707add3353455473f5ff26a117c7843d42cd4d5.
Switch to using artist rather than artists[0].
Merge NEWS items for compilation and multiartist.
Tweak NEWS (per mineo comment)
Put default script into a constant.
Add non-NAT and NAT tests
Fix default script for NAT tracks
Support ASF video file formats (reverted from commit 7494155d0c22bfb0fb479ef3613ba11a2993ec6d)
Support .ogv video files
Fix up albumartist_website plugin debug message

Traceback (most recent call last):
  File "picard\webservice.pyo", line 285, in _process_reply
  File "C:\Program Files (x86)\MusicBrainz Picard\plugins\albumartist_website.py", line 95, in website_process
    log.debug("%s: %r: Artist Official Homepages = %s", PLUGIN_NAME, artistId, url)
NameError: global name 'url' is not defined
Not having 'relation_list' is not invalid, do not emit error message

Error message is still emitted if metadata has no artist (which shouldn't happen for artist query)

E: 17:27:06 Album Artist Website: u'2451caed-5d09-456f-b640-5880b6060a64': MusicBrainz artist xml result not in correct format - {'attribs': {}, 'text': u'', 'children': {u'metadata': [{'attribs': {}, 'text': u'', 'children': {u'artist': [{'attribs': {u'type': u'Group', u'id': u'2451caed-5d09-456f-b640-5880b6060a64'}, 'text': u'', 'children': {u'name': [{'attribs': {}, 'text': u'Sir Frankie Crisp', 'children': {}}], u'sort_name': [{'attribs': {}, 'text': u'Sir Frankie Crisp', 'children': {}}]}}]}}]}}
Merge branch 'albumartist_website_fix' of https://github.com/zas/picard
Merge branch 'video' of https://github.com/phw/picard
Merge branch 'sophist_fix_default_naming_script' of https://github.com/Sophist-UK/picard