Add copyright notices.

The tool interface sucks (especially "committing" information, which is just
me doing everything by hand from the command line), but I think this is in
theory actually a viable way of describing the world. So copyright it.

cat-file.c

+/*
+ * GIT - The information manager from hell
+ *
+ * Copyright (C) Linus Torvalds, 2005
+ */
 #include "cache.h"
 
 int main(int argc, char **argv)

commit-tree.c

+/*
+ * GIT - The information manager from hell
+ *
+ * Copyright (C) Linus Torvalds, 2005
+ */
 #include "cache.h"
 
 #include <pwd.h>

init-db.c

+/*
+ * GIT - The information manager from hell
+ *
+ * Copyright (C) Linus Torvalds, 2005
+ */
 #include "cache.h"
 
 int main(int argc, char **argv)

read-cache.c

+/*
+ * GIT - The information manager from hell
+ *
+ * Copyright (C) Linus Torvalds, 2005
+ */
 #include "cache.h"
 
 const char *sha1_file_directory = NULL;

read-tree.c

+/*
+ * GIT - The information manager from hell
+ *
+ * Copyright (C) Linus Torvalds, 2005
+ */
 #include "cache.h"
 
 static int unpack(unsigned char *sha1)

show-diff.c

+/*
+ * GIT - The information manager from hell
+ *
+ * Copyright (C) Linus Torvalds, 2005
+ */
 #include "cache.h"
 
 #define MTIME_CHANGED	0x0001

update-cache.c

+/*
+ * GIT - The information manager from hell
+ *
+ * Copyright (C) Linus Torvalds, 2005
+ */
 #include "cache.h"
 
 static int cache_name_compare(const char *name1, int len1, const char *name2, int len2)

write-tree.c

+/*
+ * GIT - The information manager from hell
+ *
+ * Copyright (C) Linus Torvalds, 2005
+ */
 #include "cache.h"
 
 static int check_valid_sha1(unsigned char *sha1)