Python 3 preparation: make fallback SysCallError an actual exception class.

The code defines a fallback version of SysCallError when import of
OpenSSL.SSL.  But in Python 3, defining it as None and then using in
"except" statements results in:

TypeError: catching classes that do not inherit from BaseException is
not allowed

Author: jsm28

roundup/cgi/client.py

@@ -23,7 +23,8 @@
 try:
     from OpenSSL.SSL import SysCallError
 except ImportError:
-    SysCallError = None
+    class SysCallError(Exception):
+        pass
 
 from roundup import roundupdb, date, hyperdb, password
 from roundup.cgi import templating, cgitb, TranslationService