Set file types for abl file components.
Rename db-unit to abl-module since it may or may not deal with dbs.
Use extension-specific class for abl systems.
Use source filename for class output pathnames.

The class qualifier has to match the path, so just use the path.
Enable output translations for output pathnames.
Add component-depends-on methods for compile-op.

Propagates compile-op to child components and so forth, and avoids the
default load-op (which will fail because this ain't lisp).
Add function to set the output directory.