Java backend: implemented function Id2String
Java backend: fixed a serious bug and relaxed an assertion a little bit
Java backend: avoided performing unification between two identical terms
Java backend: asserted that the subject term must be always ground when doing concrete execution
Java backend: fixed a stupid bug on operator precedence introduced by me
tests/config: included all (modified) test programs of kool-typed-static for the Java backend
Java backend: commented out an assertion to be fixed