126.96.36.199: WHO-CALLS information for source transformed calls
* Generalize the solution used for macroexpansion XREFs to take care
of other source-level stuff: this includes both source-transforms
Fixes launchpad bug #542174.
Note re. 188.8.131.52: the commit message is erronous. The real commit
message would have noted that since FIND-OPTIONAL-DISPATCH-TYPES
doesn't rightly consider &REST mismatch a lossage in the presence of
&KEY, we need to make sure the type assigned to the leaf has a &REST
type if the function actually has a &REST argument.