bitbake/exceptions: Handle reports from the field of exception code failures

Despite using python 2.6, there have been reports of issues where
bitbake is printing tracebacks with errors in the exception handling
code. This was masking the real error.

Since we need to do whatever we can to give the user good feedback about
errors, detect the tuple instead of namedtuple case and don't fault
in the exception handler but just give up trying to traceback any further.

In the reported cases, this gives a message the user can then understand.

(Bitbake rev: 9ec0429271e68527a55fc123dea5a1b959c6ec3b)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/exceptions.py

@@ -32,7 +32,14 @@ class TracebackEntry(namedtuple.abc):
 def _get_frame_args(frame):
     """Get the formatted arguments and class (if available) for a frame"""
     arginfo = inspect.getargvalues(frame)
-    if not arginfo.args:
+
+    try:
+        if not arginfo.args:
+            return '', None
+    # There have been reports from the field of python 2.6 which doesn't 
+    # return a namedtuple here but simply a tuple so fallback gracefully if
+    # args isn't present.
+    except AttributeError:
         return '', None
 
     firstarg = arginfo.args[0]