Change 2i to use long values

The original implementation of 2i used int for _int indexes
which is caused an upper bound of 2^31. The client will
now use long values eliminating this restriction.

When possible backwards compatability was maintained, specifically
regarding the @RiakIndex annotation and the FetchIndex&lt;T&gt; class. Users of
the IRiakObject interface calling getIntIndex() or allIntIndexes()
will need to change the type being returned from Set&lt;Integer&gt; to Set&lt;Long&gt;

This addresses #112

@russelldb - If you could give this a serious looking at, it would be most appreciated.