Add print-object infrastructure for constituents (used while debugging).

Functionalize a few macros,
make constituent designators slightly more readable,
fix a typo,
fix a compiler warning in a test.

  - Added instrumentation for #. and #S
  - Potentially dangerous heuristics for defvar and defconstant
  - Improved handler for defstruct
  - New unit tests
  - Some cleanup of old code

- ADG doesn't see ASDF modules, causing ADG to mix up (:file "pkgdcl")
  in module "qres-core" with the (:file "pkgdcl") in module "pas/clr",
  for example.  The fix is to use the component-pathname instead of the
  component-name.  The component-pathname is annoyingly longer than
  the component-name however, so I'd be happy for a different solution.
- Also fixed grovel.lisp:operating-on-asdf-component-constituent to call
  signal-new-internal-symbols.  Otherwise ADG will confuse which package
  an internal symbol belongs to.

Constituents allow for more control over how dependencies are reported.  Each
constituent can depend on other constituents, but can also have subconstituents
with finer-grained dependencies.