[tex4ht] java modules

[Karl Berry]

    I attached the whole diff, but I wish to split it into several
    elementary steps.

Sounds good.

    1) the first step is that tex4ht-dir.tex is renamed to tex4ht-dir.m4
    and made a script, and the Makefile generates the texh4t-dir.tex from
    this m4 file. This way directory information is not duplicated in
    serval places, and lies only in the Makefile.

Ok, I committed tex4ht-dir.m4 and your changes to the Makefile (r716).

With a couple of changes. First, I removed the dependency on xtpipes.jar
since the .java files aren't yet created in the right place, so they
don't get compiled. Also, the javac option is -sourcepath not
--source-path, at least on my (CentOS) system.

Also, this change seemed spurious so I left it out:

-	$(update) tex4ht.env-unix $(dest_base)/unix/tex4ht.env
+	$(update) tex4ht.$env-unix $(dest_base)/unix/tex4ht.env

    Because there are several different objectives that should be each
    in a different change.

Next ... can you please send separate diffs for the following steps?
Ideally with ChangeLog entries so I don't have to write them.

We may as well skip the evidently-premature optimization of \MakeDir for
now.

OTOH, please ensure that all cd and push commands are protected
against failure, as in:
  cd somedir || exit 1
  pushd somedir || exit 1
Eitan did not bother with this, and as a result things are often
executed in the wrong directory ... --thanks, karl.