Fix imports and general cleanup

· Import from compat what comes from compat. Yes, some names are available in utils too, but that's an implementation detail.
· Use _match_id consistently whenever possible
· Fix some outdated tests
· Use consistent valid URL (always match the whole protocol, no ^ at start required)
· Use modern test definitions

youtube_dl/extractor/mofosex.py

@@ -4,7 +4,7 @@ import os
 import re
 
 from .common import InfoExtractor
-from ..utils import (
+from ..compat import (
     compat_urllib_parse_urlparse,
     compat_urllib_request,
     compat_urllib_parse,
@@ -12,7 +12,7 @@ from ..utils import (
 
 
 class MofosexIE(InfoExtractor):
-    _VALID_URL = r'^https?://(?:www\.)?(?P<url>mofosex\.com/videos/(?P<videoid>[0-9]+)/.*?\.html)'
+    _VALID_URL = r'https?://(?:www\.)?(?P<url>mofosex\.com/videos/(?P<id>[0-9]+)/.*?\.html)'
     _TEST = {
         'url': 'http://www.mofosex.com/videos/5018/japanese-teen-music-video.html',
         'md5': '1b2eb47ac33cc75d4a80e3026b613c5a',
@@ -26,7 +26,7 @@ class MofosexIE(InfoExtractor):
 
     def _real_extract(self, url):
         mobj = re.match(self._VALID_URL, url)
-        video_id = mobj.group('videoid')
+        video_id = mobj.group('id')
         url = 'http://www.' + mobj.group('url')
 
         req = compat_urllib_request.Request(url)