/*
 *  call-seq:
 *    dvector.dirty? -> _true_ or _false_
 *
 *  Returns _true_ if the vector has been modified since the last time
 *  dirty was cleared. When a Dvector is created or copied, dirty is set
 *  to false. It is set to true whenever the vector is modified. You need
 *  to reset it manually using dirty=.
 */ VALUE dvector_is_dirty(VALUE ary) {