MergeViewRows() helper function.

Merges view rows coming in on sorted channels, needed for future
commits on view memoization and _all_docs processing.
Start of couchDbAllDocs().
Views only iterator through NumPartitions.
Implemented _all_docs, capitalizing VBucket.

As part of implementing _all_docs, needed to graduate vbucket to
the capitalized VBucket so the main package can get at it.