[vimeo] Crash on password with non-ascii characters

[matmat]

youtube-dl crashes when --video-password contains an 'ö' (o with umlaut):

[debug] System config: []
[debug] User config: []
[debug] Command-line args: [u'--verbose', u'--video-password', u'PRIVATE', u'https://vimeo.com/xxxxxxxxx']
[debug] Encodings: locale UTF-8, fs UTF-8, out UTF-8, pref UTF-8
[debug] youtube-dl version 2015.11.02
[debug] Python version 2.7.10+ - Linux-4.3.0-rc7-amd64-x86_64-with-debian-stretch-sid
[debug] exe versions: avconv 2.8.1-1, avprobe 2.8.1-1, ffmpeg 2.8.1-1, ffprobe 2.8.1-1, rtmpdump 2.4
[debug] Proxy map: {}
[vimeo] xxxxxxxxx: Downloading webpage
[vimeo] xxxxxxxxx: Extracting information
Traceback (most recent call last):
File "/usr/lib/python2.7/runpy.py", line 162, in _run_module_as_main
"main", fname, loader, pkg_name)
File "/usr/lib/python2.7/runpy.py", line 72, in _run_code
exec code in run_globals
File "/usr/local/bin/youtube-dl/main.py", line 19, in
File "/usr/local/bin/youtube-dl/youtube_dl/init.py", line 410, in main
File "/usr/local/bin/youtube-dl/youtube_dl/init.py", line 400, in _real_main
File "/usr/local/bin/youtube-dl/youtube_dl/YoutubeDL.py", line 1666, in download
File "/usr/local/bin/youtube-dl/youtube_dl/YoutubeDL.py", line 661, in extract_info
File "/usr/local/bin/youtube-dl/youtube_dl/extractor/common.py", line 290, in extract
File "/usr/local/bin/youtube-dl/youtube_dl/extractor/vimeo.py", line 325, in _real_extract
File "/usr/local/bin/youtube-dl/youtube_dl/extractor/vimeo.py", line 213, in _verify_video_password
File "/usr/local/bin/youtube-dl/youtube_dl/utils.py", line 1663, in urlencode_postdata
File "/usr/lib/python2.7/urllib.py", line 1347, in urlencode
v = quote_plus(str(v))
UnicodeEncodeError: 'ascii' codec can't encode character u'\xf6' in position 2: ordinal not in range(128)