Issue #7279:  Make Decimal('nan') hashable.  Decimal('snan') remains unhashable.

Also rewrite the Decimal __hash__ method so that it doesn't rely on
float('inf') being valid: float('inf') could raise an exception on
platforms not using IEEE 754 arithmetic.
diff --git a/Misc/NEWS b/Misc/NEWS
index e9b39b7..8f36109 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -37,7 +37,8 @@
 
 - Issue #7279: Comparisons involving a Decimal signaling NaN now
   signal InvalidOperation instead of returning False.  (Comparisons
-  involving a quiet NaN are unchanged.)
+  involving a quiet NaN are unchanged.)  Also, Decimal quiet NaNs
+  are now hashable;  Decimal signaling NaNs remain unhashable.
 
 - Issue #2531: Comparison operations between floats and Decimal
   instances now return a result based on the numeric values of the