Better error messages on duplicate enum values

pep-0435.txt

@@ -300,7 +300,7 @@ You may not define two enumeration values with the same integer value::
     ...     butters = 4
     Traceback (most recent call last):
     ...
-    ValueError: Multiple enum values: 3
+    ValueError: Conflicting enums with value '3': 'kenny' and 'kyle'
 
 You also may not duplicate values in derived enumerations::
 
@@ -309,7 +309,7 @@ You also may not duplicate values in derived enumerations::
     ...     chartreuse = 2 # Oops!
     Traceback (most recent call last):
     ...
-    ValueError: Multiple enum values: 2
+    ValueError: Conflicting enums with value '2': 'green' and 'chartreuse'
 
 
 Enumeration values