Default to continuedl=True

We already do this in the CLI interface, so it should be just fine.

youtube_dl/downloader/common.py

@@ -318,7 +318,7 @@ def download(self, filename, info_dict):
         )
 
         continuedl_and_exists = (
-            self.params.get('continuedl', False) and
+            self.params.get('continuedl', True) and
             os.path.isfile(encodeFilename(filename)) and
             not self.params.get('nopart', False)
         )

youtube_dl/downloader/http.py

@@ -49,7 +49,7 @@ def real_download(self, filename, info_dict):
 
         open_mode = 'wb'
         if resume_len != 0:
-            if self.params.get('continuedl', False):
+            if self.params.get('continuedl', True):
                 self.report_resuming_byte(resume_len)
                 request.add_header('Range', 'bytes=%d-' % resume_len)
                 open_mode = 'ab'

youtube_dl/downloader/rtmp.py

@@ -105,7 +105,7 @@ def run_rtmpdump(args):
         protocol = info_dict.get('rtmp_protocol', None)
         real_time = info_dict.get('rtmp_real_time', False)
         no_resume = info_dict.get('no_resume', False)
-        continue_dl = info_dict.get('continuedl', False)
+        continue_dl = info_dict.get('continuedl', True)
 
         self.report_destination(filename)
         tmpfilename = self.temp_name(filename)