Consolidate null_sha1[].

Signed-off-by: Junio C Hamano <junio@twinsun.com>

cache.h

@@ -189,6 +189,7 @@ extern char *git_path(const char *fmt, ...) __attribute__((format (printf, 1, 2)
 extern char *sha1_file_name(const unsigned char *sha1);
 extern char *sha1_pack_name(const unsigned char *sha1);
 extern char *sha1_pack_index_name(const unsigned char *sha1);
+extern const unsigned char null_sha1[20];
 
 int git_mkstemp(char *path, size_t n, const char *template);
 

diff-files.c

@@ -34,7 +34,6 @@ static void show_modified(int oldmode, int mode,
 
 int main(int argc, const char **argv)
 {
-	static const unsigned char null_sha1[20] = { 0, };
 	const char **pathspec;
 	const char *prefix = setup_git_directory();
 	int entries, i;

diff.c

@@ -10,7 +10,6 @@
 #include "diffcore.h"
 
 static const char *diff_opts = "-pu";
-static unsigned char null_sha1[20] = { 0, };
 
 static int use_size_cache;
 
@@ -414,7 +413,7 @@ void diff_free_filespec_data(struct diff_filespec *s)
 static void prep_temp_blob(struct diff_tempfile *temp,
 			   void *blob,
 			   unsigned long size,
-			   unsigned char *sha1,
+			   const unsigned char *sha1,
 			   int mode)
 {
 	int fd;

sha1_file.c

@@ -20,6 +20,8 @@
 #endif
 #endif
 
+const unsigned char null_sha1[20] = { 0, };
+
 static unsigned int sha1_file_open_flag = O_NOATIME;
 
 static unsigned hexval(char c)