Here's the logic (mostly suggested by John Fieber):
@ If ALLLANG is defined, descend to all language-specific subdirs too.
@ If ALLLANG is not defined, but LANG is defined and a subdirectory with
that name exists, descend to that directory too.
@ In either case, the default subdirectories are always traversed.
Right now there's only one subdirectory (ja_JP.EUC) with one document
(handbook). Note these changes won't do anything if you don't have ALLLANG
defined or LANG set to ja_JP.EUC.
The make world for releases is expected to define ALLLANG, so all language-
specific documentation can be built (and be put in appropriate *dists).
This should be in 2.2.
