Rework of 'query-bulk' implementation for 0.9.x

Please see issue #378, I just reworked for latest 0.9.x branch and made configurable. Corresponding change for carbon was merged by @mleinart while ago - https://github.com/graphite-project/carbon/pull/132
PS: 
I know that 0.9.x is not intended for new features, but I use this patch in production for long time and it really helps with performance, it will be nice to have it in upstream than in own branch only. :)
Will port it to master though.