WFMF11 — Make the association between WfRequester and WfProcess optional

Summary: Section 2.6.3 and the object model in Figure 2-1 state that there must be a
WfRequester associated with each WfProcess. Registering a Requester is useful
in scenarios where some entity is actually waiting for the process to complete.
There are several scenarios where this is not the case; for example when a
process is started in a chained sub-process scenario or when a process is
primarily started because of its "side-effects" (achieved by its Activities) ,
not to retrieve its results. In this case the status queries provided by
WfProcess are sufficient to allow an administrator to observe the WfProcess.
Making Requester mandatory implies that someone must keep a persistent object
around for a potentially long time even when there is no real use for it.

I propose to make the association between WfRequester and WfProcess optional
(i.e., cardinality of "requester" would be 0..1 instead of 1).