Module and tests:
* Map conditions to related signals.
* Make contexts unhashable.
* Eliminate used "default" attribute in exception definitions.
* Eliminate the _filterfunc in favor of a straight list.

Docs:
* Eliminate documented references to conditions that are not signals.
* Eliminate parenthetical notes such as "1/0 --> Inf" which are no
  longer true with the new defaults.
diff --git a/Misc/NEWS b/Misc/NEWS
index df3dcca..b7a1ade 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -26,6 +26,9 @@
 Library
 -------
 
+- decimal.py now only uses signals in the spec.  The other conditions are
+  no longer part of the public API.
+
 Tools/Demos
 -----------