Add support for DR-P2 radio

[morris-classical]

It is a classical music radio in Denmark (audio only). Here's the error I get when trying to get a concert from there.

[debug] System config: []
[debug] User config: []
[debug] Command-line args: ['http://www.dr.dk/radio/ondemand/p2/p2-operaaften-81', '--verbose']
[debug] Encodings: locale UTF-8, fs utf-8, out UTF-8, pref UTF-8
[debug] youtube-dl version 2014.08.02.1
[debug] Python version 2.7.2 - Darwin-10.8.0-x86_64-i386-64bit
[debug] Proxy map: {}
[generic] p2-operaaften-81: Requesting header
WARNING: Falling back on generic information extractor.
[generic] p2-operaaften-81: Downloading webpage
[generic] p2-operaaften-81: Extracting information
ERROR: Unsupported URL: http://www.dr.dk/radio/ondemand/p2/p2-operaaften-81; please report this issue on https://yt-dl.org/bug . Be sure to call youtube-dl with the --verbose flag and include its complete output. Make sure you are using the latest version; type youtube-dl -U to update.
Traceback (most recent call last):
File "/usr/local/bin/youtube-dl/youtube_dl/extractor/generic.py", line 457, in _real_extract
doc = parse_xml(webpage)
File "/usr/local/bin/youtube-dl/youtube_dl/utils.py", line 1420, in parse_xml
return xml.etree.ElementTree.XML(s.encode('utf-8'), **kwargs)
File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/xml/etree/ElementTree.py", line 1282, in XML
parser.feed(text)
File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/xml/etree/ElementTree.py", line 1624, in feed
self._raiseerror(v)
File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/xml/etree/ElementTree.py", line 1488, in _raiseerror
raise err
ParseError: not well-formed (invalid token): line 147, column 140
Traceback (most recent call last):
File "/usr/local/bin/youtube-dl/youtube_dl/YoutubeDL.py", line 516, in extract_info
ie_result = ie.extract(url)
File "/usr/local/bin/youtube-dl/youtube_dl/extractor/common.py", line 170, in extract
return self._real_extract(url)
File "/usr/local/bin/youtube-dl/youtube_dl/extractor/generic.py", line 752, in _real_extract
raise ExtractorError('Unsupported URL: %s' % url)
ExtractorError: Unsupported URL: http://www.dr.dk/radio/ondemand/p2/p2-operaaften-81; please report this issue on https://yt-dl.org/bug . Be sure to call youtube-dl with the --verbose flag and include its complete output. Make sure you are using the latest version; type youtube-dl -U to update.