+ /* [i..hunk_end) are interesting. Now is it really
+ * interesting? We check if there are only two versions
+ * and the result matches one of them. That is, we look
+ * at:
+ * (+) line, which records lines added to which parents;
+ * this line appears in the result.
+ * (-) line, which records from what parents the line
+ * was removed; this line does not appear in the result.
+ * then check the set of parents the result has difference
+ * from, from all lines. If there are lines that has
+ * different set of parents that the result has differences
+ * from, that means we have more than two versions.
+ *
+ * Even when we have only two versions, if the result does
+ * not match any of the parents, the it should be considered
+ * interesting. In such a case, we would have all '+' line.
+ * After passing the above "two versions" test, that would
+ * appear as "the same set of parents" to be "all parents".