Here's a patch:

  - comparisons between a Decimal and float produce a result based
    on the numeric values of the Decimal and float

  - change Decimal.__hash__ so that floats and Decimals with (exactly)
    equal value have the same hash.  This preserves the rule that if
    two objects compare equal then they hash equal.

  - add tests, and update documentation.

Still open:  should this change be forward ported to py3k?  If not, then these comparisons should produce a DeprecationWarning.