Addendum to r30531:

 * Fix some comments
 * Fix some spacing in the non-verbose "make" output
 * Make javadoc non-verbose output like other non-verbose output
 * Remove the use of JAVA_CLASS_FILES; it wasn't correct any way (it
   both derived names from JAVA_SRC_FILES ''and'' used mpi/*.class, so
   many files were listed twice)
 * Move the generation of javadoc files to "make" time (vs. "make
   install" time) by putting the "doc" subdirectory in BUILT_SOURCES
 * Make doc dependent upon mpi/MPI.class, not mpi.jar -- we only need
   the classes to exist, not the final jarfile.
 * Make jdoc-install dependent upon a real build artifact (the doc
   dir), not an artificial name that will never exist (jdoc)
 * Separate the removal of the doc (and mpi) subdirectories during
   "make clean" off into the clean-local target, because CLEANFILES
   can really only had ''files'' added to it.

These changes also fix parallel builds.

cmr=v1.7.5:ticket=#4214