GOCBC-99: Correct issue with use of Cas and MutationTokens.
GOCBC-99: Correct issue with use of Cas and MutationTokens.

Change-Id: I80b6b4b1b2b76f236b4f26cef6ac541c8fbce41f
Reviewed-on: http://review.couchbase.org/59992
Reviewed-by: Sergey Avseyev <87f6d5e4fd3644c3c20800cde7fd3ad1569370b3@gmail.com>
Tested-by: Brett Lawson <c8c4369773d7d7226e031f0c4af62e3f38a08510@gmail.com>

brett19/gocb