allow a WriteCondHandle's range to be automatically set from the intersection of the ranges of any number of ReadCondHandles. Provides a new WriteCondHandle::record( T* ) method that doesn't take a range. If this method is used but no dependencies have been set, will return an error.
also adds the method getRange() to ReadCondHandles and WriteCondHandles.
adds a test in StoreGate/test, and expands the example in AthenaExamples/AthExHive