+ * Answers true if this object is either equivalent to, or can be 'improved'
+ * by, the given entry. Specifically, answers true if
+ * <ul>
+ * <li>source and accession are identical</li>
+ * <li>version is identical, or this version is of the format "someSource:0",
+ * in which case the version for the other entry replaces it</li>
+ * <li>mappings are not compared but if this entry has no mapping, replace
+ * with that for the other entry</li>
+ * </ul>