correct type of EMPTY_TREE_SHA1_BIN

Functions such as hashcmp that expect a binary SHA-1 value take
parameters of type "unsigned char *" to avoid accepting a textual
SHA-1 passed by mistake.  Unfortunately, this means passing the string
literal EMPTY_TREE_SHA1_BIN requires an ugly cast.  Tweak the
definition of EMPTY_TREE_SHA1_BIN to produce a value of more
convenient type.

In the future the definition might change to

	extern const unsigned char empty_tree_sha1_bin[20];
	#define EMPTY_TREE_SHA1_BIN empty_tree_sha1_bin

Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/checkout.c

@@ -404,7 +404,7 @@ static int merge_working_tree(struct checkout_opts *opts,
 		topts.dir->exclude_per_dir = ".gitignore";
 		tree = parse_tree_indirect(old->commit ?
 					   old->commit->object.sha1 :
-					   (unsigned char *)EMPTY_TREE_SHA1_BIN);
+					   EMPTY_TREE_SHA1_BIN);
 		init_tree_desc(&trees[0], tree->buffer, tree->size);
 		tree = parse_tree_indirect(new->commit->object.sha1);
 		init_tree_desc(&trees[1], tree->buffer, tree->size);

cache.h

@@ -676,9 +676,11 @@ static inline void hashclr(unsigned char *hash)
 
 #define EMPTY_TREE_SHA1_HEX \
 	"4b825dc642cb6eb9a060e54bf8d69288fbee4904"
-#define EMPTY_TREE_SHA1_BIN \
+#define EMPTY_TREE_SHA1_BIN_LITERAL \
 	 "\x4b\x82\x5d\xc6\x42\xcb\x6e\xb9\xa0\x60" \
 	 "\xe5\x4b\xf8\xd6\x92\x88\xfb\xee\x49\x04"
+#define EMPTY_TREE_SHA1_BIN \
+	 ((const unsigned char *) EMPTY_TREE_SHA1_BIN_LITERAL)
 
 int git_mkstemp(char *path, size_t n, const char *template);
 

notes-merge.c

@@ -615,7 +615,7 @@ int notes_merge(struct notes_merge_options *o,
 	bases = get_merge_bases(local, remote, 1);
 	if (!bases) {
 		base_sha1 = null_sha1;
-		base_tree_sha1 = (unsigned char *)EMPTY_TREE_SHA1_BIN;
+		base_tree_sha1 = EMPTY_TREE_SHA1_BIN;
 		OUTPUT(o, 4, "No merge base found; doing history-less merge");
 	} else if (!bases->next) {
 		base_sha1 = bases->item->object.sha1;

sha1_file.c

@@ -52,7 +52,7 @@ static struct cached_object {
 static int cached_object_nr, cached_object_alloc;
 
 static struct cached_object empty_tree = {
-	EMPTY_TREE_SHA1_BIN,
+	EMPTY_TREE_SHA1_BIN_LITERAL,
 	OBJ_TREE,
 	"",
 	0