Removing the "RiakVectorClock" annotation: too dangerous to keep around.

Basically, annotating an object with @RiakVectorClock and keeping it around
(in a cache, or wherever) then saving it again will create siblings, if
other writes have occurred.

It's a lot safer to simply NEVER annotate objects with @RiakVectorClock,
and let users keep track of the vector clock (if they want to) through
the Response and StoreRequest objects.
Start header processing.
Move index header parsing to "Index" (align with "Resource").
Improve testing.
Fixes from testing.