Modified get_all_hits() to enable the specification of response groups.
Modified build_list_params to support both an array of parameter names, or
a string containing a set of whitespace- or comma-delimited parameter names.
Formerly, only a single parameter name could be accepted as a string.

This change was submitted with a pull request on 11/27/2012, but was inadvertently removed, I believe, on 12/5 as part of fixing a regression with ec2.
As of September 2012, Amazon modified the 2012-03-25 API such that it has now deprecated the REST and SOAP notification protocols; and to inform us of that fact they are no longer signing their REST and SOAP notification messages. The signature keyword now instead returns:
    Signature: u'DEPRECATED'
So we are now always returning True in this case so as not to break existing code.
Re-added WSDL definition that was inadvertently removed.
Merge branch 'develop' of https://github.com/dmcritchie/boto into develop