dl_database: use openurl in place of requests.

Note that this will avoid downloading the index since its contents are
not used.

Furthermore, when trying to enumerate annotation files, this will
handle errors other than 404 errors, and raise an exception as
appropriate.

Author: Benjamin Moody

wfdb/io/record.py

@@ -4528,8 +4528,7 @@ def dl_database(db_dir, dl_dir, records='all', annotators='all',
         db_dir = posixpath.join(db_dir, get_version(db_dir))
     db_url = posixpath.join(download.PN_CONTENT_URL, db_dir) + '/'
     # Check if the database is valid
-    r = requests.get(db_url)
-    r.raise_for_status()
+    _url.openurl(db_url, check_access=True)
 
     # Get the list of records
     record_list = download.get_record_list(db_dir, records)
@@ -4586,10 +4585,11 @@ def dl_database(db_dir, dl_dir, records='all', annotators='all',
             for a in annotators:
                 ann_file = rec+'.'+a
                 url = posixpath.join(download.config.db_index_url, db_dir, ann_file)
-                rh = requests.head(url)
-
-                if rh.status_code != 404:
+                try:
+                    _url.openurl(url, check_access=True)
                     all_files.append(ann_file)
+                except FileNotFoundError:
+                    pass
 
     dl_inputs = [(os.path.split(file)[1], os.path.split(file)[0], db_dir, dl_dir, keep_subdirs, overwrite) for file in all_files]