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· Fix some outdated tests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/downloader/f4m.py

@@ -9,10 +9,12 @@ import xml.etree.ElementTree as etree
 
 from .common import FileDownloader
 from .http import HttpFD
+from ..compat import (
+    compat_urlparse,
+)
 from ..utils import (
     struct_pack,
     struct_unpack,
-    compat_urlparse,
     format_bytes,
     encodeFilename,
     sanitize_open,