Fix in NewChunk compression. Sparse new chunk representation can have 0s among stored values (result of calling set()) which cause assertion failure. Instead of asserting on exactly the non zeros being stored, added code to filter zeros out when compressing.
Merge branch 'master' of github.com:0xdata/h2o
updated Typeahead request to run faster when there are many (non-user) keys in K/V store:
   1) global keys are now fetch using new task, which uses faster lower-level interface to K/V store and fetches keys and information about keys locally as the result of the task rather then invoking TaskSendKey for each user key.
   2) user keys (+ their type and size info) are now cached locally in separate cache which is updated only once in a while.
Merge branch 'master' of github.com:0xdata/h2o