Whitespace.
added support for recognizing vbuckets in rest_couch

cbugg: bug-446
support bucket_uuid in couch_rest get db

cbugg: close bug-446
Implementation of _stats

cbugg: close bug-448
Remove sum() javascript helper.

I needed this in my javascript _count and _sum implementations,
but I don't anymore.  In case we need it again, it's still in git
history.
Whitespace again.
Refactored out bucket_stats.go file.
Generic StatsSnapshot interface, to Statish interface is generic.

This is in preparation for having server-level stats in addition to
bucket-level stats.
Moved bucket related stats to bucket_stats.go file.

And got rid of stats_util.go, as generic stats stuff is now in
stats.go file.
Refactored out vbucket_mutation.go file.