ll_union_merge(): rename path_unused parameter

The "path" parameter to ll_union_merge() is named "path_unused", since
we don't ourselves use it. But we do pass it to ll_xdl_merge(), which
may look at it (it gets passed to ll_binary_merge(), which may pass it
to warning()). Let's rename it to correct this inaccuracy (both of the
other functions correctly do not call this "unused").

Note that we also pass drv_unused, but it truly is unused by the rest of
the stack (it only exists at all to provide a generic interface that
matches what ll_ext_merge() needs).

Reported-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

ll-merge.c

@@ -138,7 +138,7 @@ static int ll_xdl_merge(const struct ll_merge_driver *drv_unused,
 
 static int ll_union_merge(const struct ll_merge_driver *drv_unused,
 			  mmbuffer_t *result,
-			  const char *path_unused,
+			  const char *path,
 			  mmfile_t *orig, const char *orig_name,
 			  mmfile_t *src1, const char *name1,
 			  mmfile_t *src2, const char *name2,
@@ -150,7 +150,7 @@ static int ll_union_merge(const struct ll_merge_driver *drv_unused,
 	assert(opts);
 	o = *opts;
 	o.variant = XDL_MERGE_FAVOR_UNION;
-	return ll_xdl_merge(drv_unused, result, path_unused,
+	return ll_xdl_merge(drv_unused, result, path,
 			    orig, orig_name, src1, name1, src2, name2,
 			    &o, marker_size);
 }