Addresses #1956 refs[t:1956] Add c_getf_set_range_reverse, c_getf_get_both_range_reverse, (and c_get versions)
Equivalent to non-reverse but just changes the search direction

git-svn-id: file:///svn/toku/tokudb@14086 c7de825b-a66e-492c-adef-691d508d4ae1