(#85) - view names without slashes
(#58) - proper behavior for _sum

The built-in _sum function should return
an error if the values are not numbers or
number arrays.  Also, it should support number
arrays.
(#104) - add test for cleanup of duplicate indexes
(#107) - remove fixme comment
(#105) - batch the persisted mapreduce updates

This batches the updates fetched from db.changes()
to a max batch size of 50 (may change later) in order
to avoid reading every document into memory.