Bugfix: Avoid duplicate mutations, reset accumulator.

Accumulator was reset after time threshold, but not after buffer threshold.

- added switch StreamClient to catch duplicate StreamBegin.
- consolidated logging at StreamClient for vbmap.
- logging changed to debug.go

Change-Id: I5d3bcac1c6f15b6289fc2936474c37ffcb224309
Reviewed-on: http://review.couchbase.org/39048
Reviewed-by: Deepkaran Salooja <deepkaran.couchbase@gmail.com>
Reviewed-by: Pratap Chakravarthy <prataprc@couchbase.com>
Tested-by: Pratap Chakravarthy <prataprc@couchbase.com>
Bugfix: race between StreamBegin and StreamSync.

kvfeed will spawn a vbucket-routine when it sees StreamBegin for that vbucket.
Immediately after that it was posting the StreamBegin Event to newly spawned
routine.

Race happens when kvfeed is switched out after it spawned the routine but
before posting the event. The new vbucket-routine gets a chance to run and
starts emitting the heartbeat for every 5ms. Leading to StreamSync before
StreamBegin.

- feed does not send vbmap now. StreamBegin is the sole event that opens the
  path for a vbucket.

Change-Id: Ic93c72f087d336af9d587f85b0e2e949b2f739b6
Reviewed-on: http://review.couchbase.org/39049
Reviewed-by: Deepkaran Salooja <deepkaran.couchbase@gmail.com>
Reviewed-by: Pratap Chakravarthy <prataprc@couchbase.com>
Tested-by: Pratap Chakravarthy <prataprc@couchbase.com>
Added 1024 vbuckets for datapath.go

Change-Id: Iab2562a3a82932d87f0020f01bd25c8c540b7d88
Reviewed-on: http://review.couchbase.org/39050
Reviewed-by: Deepkaran Salooja <deepkaran.couchbase@gmail.com>
Reviewed-by: Pratap Chakravarthy <prataprc@couchbase.com>
Tested-by: Pratap Chakravarthy <prataprc@couchbase.com>