Issue #13701: Fix decorator avoidance (due to desire for Python 2.3...

Issue #13701: Fix decorator avoidance (due to desire for Python 2.3 compatibility) in decimal module.

Lib/decimal.py

@@ -703,8 +703,7 @@ class Decimal(object):
 
         raise TypeError("Cannot convert %r to Decimal" % value)
 
-    # @classmethod, but @decorator is not valid Python 2.3 syntax, so
-    # don't use it (see notes on Py2.3 compatibility at top of file)
+    @classmethod
     def from_float(cls, f):
         """Converts a float to a decimal number, exactly.
 
@@ -743,7 +742,6 @@ class Decimal(object):
             return result
         else:
             return cls(result)
-    from_float = classmethod(from_float)
 
     def _isnan(self):
         """Returns whether the number is not actually one.