warnings.warn_explicit() did not have the proper TypeErrors in place to prevent

bus errors or SystemError being raised. As a side effect of fixing this, a bad
DECREF that could be triggered when 'message' and 'category' were both None was
fixed.

Closes issue 3211. Thanks JP Calderone for the bug report.

Lib/warnings.py

@@ -202,6 +202,7 @@ def warn(message, category=None, stacklevel=1):
 
 def warn_explicit(message, category, filename, lineno,
                   module=None, registry=None, module_globals=None):
+    lineno = int(lineno)
     if module is None:
         module = filename or "<unknown>"
         if module[-3:].lower() == ".py":