java: allow both JAVA and nobase_JAVA in the same Makefile.am

java: allow both JAVA and nobase_JAVA in the same Makefile.am

* automake.in (handle_java): Also strip `nobase_' from the given
prefix, when needed.
* tests/java-clean.test: Update and extend.
* tests/java-compile-install.test: Likewise.
* tests/java-no-duplicate.test: Likewise.
* tests/java-sources.test: Likewise.
* tests/java-noinst.test: Likewise.
* tests/java-mix-dist-nodist.test: Renamed to ...
* tests/java-mix.test: ... this, and extended.
* tests/java-nobase.test: New test, still xfailing due to
unrelated issues.
* tests/Makefile.am (TESTS, XFAIL_TESTS): Update.