Fix the Krati entries iterator to properly handle key collisions.

When using Krati the Fetch command does not always return the expected number of key/value pairs.  The larger the store the more likely that the number of key/value pairs returned would be less than expected.  I tracked this issue down to what I think is a very simple bug in the KratiStorageEngine code - if there are key collisions at an index then the current iterator returned by the call to the entries method only returns the first key at that index.

This update contains a fix for this problem and a new test case that demonstrates the problem.