SPY-144: Avoid growing callstack on get* clones.

This changeset makes sure that if an operation gets cloned over
and over again (which is not the norm, but can happen in certain
failure scenarios), it will not lead to a stack overflow.

Special thanks to Kirill Safonov for pointing out the right fix.

Change-Id: I6846fe9b23d43d9f2e257a5206a511f941aed8ff
Reviewed-on: http://review.couchbase.org/30415
Reviewed-by: Michael Nitschinger <michael.nitschinger@couchbase.com>
Tested-by: Michael Nitschinger <michael.nitschinger@couchbase.com>