ll-merge: warn about inability to merge binary files only when we can't

When a path being merged is auto detected to be a binary file, we
warned "Cannot merge binary files" before switching to activate the
binary ll-merge driver.  When we are merging with the -Xours/theirs
option, however, we know what the "clean" merge result is, and the
warning is inappropriate.

In addition, when the path is explicitly marked as a binary file,
this warning was not issued, even though without -Xours/theirs, we
cannot cleanly automerge such a path, which was inconsistent.

Move the warning code from ll_xdl_merge() to ll_binary_merge(), and
issue the message only when we cannot cleanly automerge.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

ll-merge.c

@@ -35,7 +35,7 @@ struct ll_merge_driver {
  */
 static int ll_binary_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,
@@ -53,6 +53,9 @@ static int ll_binary_merge(const struct ll_merge_driver *drv_unused,
 	} else {
 		switch (opts->variant) {
 		default:
+			warning("Cannot merge binary files: %s (%s vs. %s)\n",
+				path, name1, name2);
+			/* fallthru */
 		case XDL_MERGE_FAVOR_OURS:
 			stolen = src1;
 			break;
@@ -88,8 +91,6 @@ static int ll_xdl_merge(const struct ll_merge_driver *drv_unused,
 	if (buffer_is_binary(orig->ptr, orig->size) ||
 	    buffer_is_binary(src1->ptr, src1->size) ||
 	    buffer_is_binary(src2->ptr, src2->size)) {
-		warning("Cannot merge binary files: %s (%s vs. %s)\n",
-			path, name1, name2);
 		return ll_binary_merge(drv_unused, result,
 				       path,
 				       orig, orig_name,