Sort range keys in FakeDynamo before selection

Hello @x-ma, @giannic, 

Please review the following commits I made in branch 'satya-secondaryIndex'.

8605892940ea1655eba11822e0a2fc1248de7982 (2014-08-29 12:56:46 -0700)
Sort range keys in FakeDynamo before selection

R=@x-ma
R=@giannic