Make "hashable" a glossary entry and clarify docs on __cmp__, __eq__ and __hash__.
I hope the concept of hashability is better understandable now.
Thanks to Tim Hatch for pointing out the flaws here.
diff --git a/Doc/library/datetime.rst b/Doc/library/datetime.rst
index 24d4f69..9442d29 100644
--- a/Doc/library/datetime.rst
+++ b/Doc/library/datetime.rst
@@ -262,7 +262,7 @@
comparison is ``==`` or ``!=``. The latter cases return :const:`False` or
:const:`True`, respectively.
-:class:`timedelta` objects are hashable (usable as dictionary keys), support
+:class:`timedelta` objects are :term:`hashable` (usable as dictionary keys), support
efficient pickling, and in Boolean contexts, a :class:`timedelta` object is
considered to be true if and only if it isn't equal to ``timedelta(0)``.