Fixes to get pipelined client requests working better. Need a function

Fixes to get pipelined client requests working better.  Need a function
called storeClientPending() whose purpose is to tell the client side
if there is already a callback registered for the entry and the client.
If not, then we'll register one via storeClientCopy().  This is due to
a race condition; when we have pipelined requests, we can not guarantee
that we'll get Deferred in clientSendMoreData() before its time to
send the object off to the client, so the original handler may still
be in place.