Adds yet another magic function "SCYLLA_COUNTER_SHARD_LIST", indicating that
argument value, which must be a list of tuples <int, UUID, long, long>,
should be inserted as an actual counter value, not update.
This of course to allow counters to be read from sstable loader.
Note that we also need to allow timestamps for counter mutations,
as well as convince the counter code itself to treat the data as
already baked. So ugly wormhole galore.
v2:
* Changed flag names
* More explicit wormholing, bypassing normal counter path, to
avoid read-before-write etc
* throw exceptions on unhandled shard types in marshalling
v3:
* Added counter id ordering check
* Added batch statement check for mixing normal and raw counter updates
Message-Id: <1487683665-23426-2-git-send-email-calle@scylladb.com>