build: Overhaul auto-detection of Java when JAVA_HOME is not set. * build-aux/OctJavaQry.class: Compiled code to help configure determine installation directories. Exported in tarball. * build-aux/OctJavaQry.java: Java code to help configure determine installation directories. * Makefile.am: Export OctJavaQry.class code in tarball. * configure.ac: If JAVA_HOME is unset, attempt to find a Java executable. Use java executable and Java code to try and determine necessary directories. * libinterp/octave-value/ov-java.cc: Use JAVA_LDPATH variable to find libjvm.

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