+### The `DUMPERS' list consists of (PREDICATE, LISTERS) pairs. The PREDICATE
+### is a function of one argument -- a directory name -- which returns true
+### if the LISTERS should be used to enumerate that directory. The LISTERS
+### are a list of functions of one argument -- again, the directory name --
+### which should return an iterable of files within that directory, relative
+### to its top-level. Lister functions should not return the root directory,
+### because it should obviously only be included once. Instead, the root is
+### handled separately by `dump_dir'.
+