Inspired by SF patch #860326, make the exception formatting by
traceback.py be closer to the built-in formatting.
A few unittests had to be fixed, too.
diff --git a/Lib/decimal.py b/Lib/decimal.py
index a8fde82..99c0de6 100644
--- a/Lib/decimal.py
+++ b/Lib/decimal.py
@@ -85,7 +85,7 @@
   ...
   ...
   ...
-DivisionByZero: x / 0
+decimal.DivisionByZero: x / 0
 >>> c = Context()
 >>> c.traps[InvalidOperation] = 0
 >>> print c.flags[InvalidOperation]
@@ -103,7 +103,7 @@
   ...
   ...
   ...
-InvalidOperation: 0 / 0
+decimal.InvalidOperation: 0 / 0
 >>> print c.flags[InvalidOperation]
 1
 >>> c.flags[InvalidOperation] = 0