Return correct value for ischar() predicate test on octave_java objects. * libinterp/octave-value/ov-java.h(is_string): Rename is_string() to is_java_string. Leave only prototype in .h file. * libinterp/octave-value/ov-java.cc(is_java_string): Move code for is_string from ov-java.h to is_java_string in ov-java.cc.