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· Fix some outdated tests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/common.py

@@ -5,8 +5,8 @@ import re
 import sys
 import time
 
+from ..compat import compat_str
 from ..utils import (
-    compat_str,
     encodeFilename,
     format_bytes,
     timeconvert,

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,

youtube_dl/downloader/hls.py

@@ -6,9 +6,11 @@ import subprocess
 
 from ..postprocessor.ffmpeg import FFmpegPostProcessor
 from .common import FileDownloader
-from ..utils import (
+from ..compat import (
     compat_urlparse,
     compat_urllib_request,
+)
+from ..utils import (
     check_executable,
     encodeFilename,
 )

youtube_dl/downloader/http.py

@@ -4,11 +4,12 @@ import os
 import time
 
 from .common import FileDownloader
-from ..utils import (
+from ..compat import (
     compat_urllib_request,
     compat_urllib_error,
+)
+from ..utils import (
     ContentTooShortError,
-
     encodeFilename,
     sanitize_open,
     format_bytes,

youtube_dl/downloader/rtmp.py

@@ -7,9 +7,9 @@ import sys
 import time
 
 from .common import FileDownloader
+from ..compat import compat_str
 from ..utils import (
     check_executable,
-    compat_str,
     encodeFilename,
     format_bytes,
     get_exe_version,