index lookups: Range and prefix queries now return result sets rather than...

index lookups: Range and prefix queries now return result sets rather than iterators. In addition to the range of functions provided by an iterator, a result set can explicitly free any resources attached to the lookup, which keeps the memory footprint as low as possible.

git-svn-id: https://babudb.googlecode.com/svn/trunk@369 d4c7dd96-b7b2-11dd-893d-d98698f66bbf