Work around issue with pickling of traceback objects

(Bitbake rev: 82928613256bad92fde9f4071244a53e20fc89ee)

Signed-off-by: Chris Larson <chris_larson@mentor.com>
Signed-off-by: Richard Purdie <rpurdie@linux.intel.com>

bitbake/lib/bb/__init__.py

@@ -29,6 +29,7 @@ if sys.version_info < (2, 6, 0):
 
 import os
 import logging
+import traceback
 
 class NullHandler(logging.Handler):
     def emit(self, record):
@@ -50,6 +51,9 @@ class BBLogger(Logger):
     def verbose(self, msg, *args, **kwargs):
         return self.log(logging.INFO - 1, msg, *args, **kwargs)
 
+    def exception(self, msg, *args, **kwargs):
+        return self.critical("%s\n%s" % (msg, traceback.format_exc()), *args, **kwargs)
+
 logging.raiseExceptions = False
 logging.setLoggerClass(BBLogger)