java: allow both dist_JAVA and nodist_JAVA in the same Makefile.am

java: allow both dist_JAVA and nodist_JAVA in the same Makefile.am

Fixes automake bug#8434.

* automake.in (handle_java): Strip `dist_' and `nodist_' from
the given prefix.  Define a new internal Makefile variable
`am__java_sources'.  Related adjustments.
* lib/am/java.am (JAVAC, JAVAROOT, CLASSPATH_ENV): Define only the
first time this am file is processed.
(class%DIR%.stamp): Stamp file renamed ...
(class%NDIR%.stamp): ... to this, so that the `dist_' and `nodist_'
prefixes are stripped from the name of the stampfile.  Adjust
declaration of dependencies by using the new automake-generated
internal variable `$(am__java_sources)'.  In the rule, use `$@'
as the name of the target, rather than hard-coding it.
* tests/java.test: Update and extend.
* tests/java-no-duplicate.test: New test.
* tests/java-mix-dist-nodist.test: Likewise.
* tests/java-compile-and-install.test: Likewise.
* tests/java-clean.test: Likewise.
* tests/java-sources.test: Likewise.
* tests/Makefile.am (TESTS): Update.