Issue #16714: use 'raise' exceptions, don't 'throw'.

Patch by Serhiy Storchaka.
diff --git a/Lib/test/test_imaplib.py b/Lib/test/test_imaplib.py
index 15b0ea0..2b2213d 100644
--- a/Lib/test/test_imaplib.py
+++ b/Lib/test/test_imaplib.py
@@ -79,7 +79,7 @@
                         return
                     line += part
                 except IOError:
-                    # ..but SSLSockets throw exceptions.
+                    # ..but SSLSockets raise exceptions.
                     return
                 if line.endswith('\r\n'):
                     break