Ref. loop created and broken

[mdavidsaver]

From the discussion in epics-base/pvAccessCPP#60 I've looked for code using PVA.

@msekoranja states that a Requester should never hold a strong reference (shared_ptr) to the associated Operation. Doing so creates a reference loop which must be explicitly broken as the Operation holds a strong ref. to its Requester. For example, in testTop/dbPv/src/testDbPv.cpp where MyRequester does so for both Channel and ChannelGet. I don't think there is a leak as ->destroy() is called to explicitly break the loop. Still, one of the few example someone might find, and it's not best practice.