WIP: Simplified channel change tracker
Better changeCache locking. Shut down goroutine on close.
Set conflict flags properly in changes feed entries

NOTE: This changes the structure of a stored document -- instead of a
"deleted" property it now has "flags".
change_cache now recovers from missing sequences after a few seconds
Keep changeCache from worrying about unused sequences generated during update
changeCache: Added expvars to track performance metrics.
Backward compatibility with the old 'deleted' document property
Make the unit tests pass.
changeCache: Ignore old echoed Tap entries at startup. Log bucket #s.
changeCache: Feed view results back into cache 
Use numbers as public sequence IDs!!
Cleaned up 'channels' view. Optimized ?conflicts and ?include_docs options
changeCache: Fixed an edge case where view is newer than Tap
Fixed Walrus submodule revision
Ignore duplicate Tap entries (from replica nodes in db cluster)
WIP: Cleanup (merged the two LogEntry structs) and fixing unit tests.
changeCache: Split out channelCache class.
Optimized channelCache (tracks firstSeq)
changeCache: Keep expvar counter of view queries
Improved algorithms in channelCache

Fixes an edge case where it would attempt to get a negative range of
sequences from the view.