Show module dependencies

[Stephan Bergmann]

With the need for dmake and build.pl almost gone, I assume that we will 
want to dump */prj/build.lst files and expressing inter-module 
dependencies via them, too.  That leaves the question how we want to be 
able to track inter-module dependencies in the future.  Specifically, 
what I am looking for is a command (e.g., make target) to show all the 
modules that some given module depends on, to help me decide into which 
module to put newly developed functionality.  (Even if this information 
were no longer relevant for gbuild---what is the future story of "make 
<module>.all"?---we will IMO nevertheless want to keep module 
dependencies from turning into a cyclic ball.)

(Btw, top-level "make help" advertises "showdeliverables" and 
"showmodules" targets, the latter of which looks relevant here, but 
neither of them works.)

Stephan