Fix any_param to work with a time attribute

When a TimeType is used, the 'ANY_PARAM' string will fail to parse
(producing an 'invalid date' ArgumentError from sunspot/type.rb:236).
any_param now responds to .utc with the current time.
Merge pull request #1 from unboxed/any_param_date_fix_cherry_pick

Fix any_param to work with a time attribute