Rename git core commands to be "git-xxxx" to avoid name clashes.

This also regularizes the make. The source files themselves don't get
the "git-" prefix, because that's just inconvenient. So instead we just
make the rule that "git-xxxx" depends on "xxxx.c", and do that for
all the core programs (ie the old "git-mktag.c" got renamed to just
"mktag.c" to match everything else).

And "show-diff" got renamed to "git-diff-files" while at it, since
that's what it really should be to match the other git-diff-xxx cases.

diff-files.c

@@ -0,0 +1,135 @@
+/*
+ * GIT - The information manager from hell
+ *
+ * Copyright (C) Linus Torvalds, 2005
+ */
+#include "cache.h"
+#include "diff.h"
+
+static const char *show_diff_usage =
+"show-diff [-p] [-q] [-r] [-z] [paths...]";
+
+static int generate_patch = 0;
+static int line_termination = '\n';
+static int silent = 0;
+
+static int matches_pathspec(struct cache_entry *ce, char **spec, int cnt)
+{
+	int i;
+	int namelen = ce_namelen(ce);
+	for (i = 0; i < cnt; i++) {
+		int speclen = strlen(spec[i]);
+		if (! strncmp(spec[i], ce->name, speclen) &&
+		    speclen <= namelen &&
+		    (ce->name[speclen] == 0 ||
+		     ce->name[speclen] == '/'))
+			return 1;
+	}
+	return 0;
+}
+
+static void show_unmerge(const char *path)
+{
+	if (generate_patch)
+		diff_unmerge(path);
+	else
+		printf("U %s%c", path, line_termination);
+}
+
+static void show_file(int pfx, struct cache_entry *ce)
+{
+	if (generate_patch)
+		diff_addremove(pfx, ntohl(ce->ce_mode), ce->sha1,
+			       ce->name, NULL);
+	else
+		printf("%c%06o\t%s\t%s\t%s%c",
+		       pfx, ntohl(ce->ce_mode), "blob",
+		       sha1_to_hex(ce->sha1), ce->name, line_termination);
+}
+
+static void show_modified(int oldmode, int mode,
+			  const char *old_sha1, const char *sha1,
+			  char *path)
+{
+	char old_sha1_hex[41];
+	strcpy(old_sha1_hex, sha1_to_hex(old_sha1));
+
+	if (generate_patch)
+		diff_change(oldmode, mode, old_sha1, sha1, path, NULL);
+	else
+		printf("*%06o->%06o\tblob\t%s->%s\t%s%c",
+		       oldmode, mode, old_sha1_hex, sha1_to_hex(sha1), path,
+		       line_termination);
+}
+
+int main(int argc, char **argv)
+{
+	static const char null_sha1[20] = { 0, };
+	int entries = read_cache();
+	int i;
+
+	while (1 < argc && argv[1][0] == '-') {
+		if (!strcmp(argv[1], "-p"))
+			generate_patch = 1;
+		else if (!strcmp(argv[1], "-q"))
+			silent = 1;
+		else if (!strcmp(argv[1], "-r"))
+			; /* no-op */
+		else if (!strcmp(argv[1], "-s"))
+			; /* no-op */
+		else if (!strcmp(argv[1], "-z"))
+			line_termination = 0;
+		else
+			usage(show_diff_usage);
+		argv++; argc--;
+	}
+
+	/* At this point, if argc == 1, then we are doing everything.
+	 * Otherwise argv[1] .. argv[argc-1] have the explicit paths.
+	 */
+	if (entries < 0) {
+		perror("read_cache");
+		exit(1);
+	}
+
+	for (i = 0; i < entries; i++) {
+		struct stat st;
+		unsigned int oldmode, mode;
+		struct cache_entry *ce = active_cache[i];
+		int changed;
+
+		if (1 < argc &&
+		    ! matches_pathspec(ce, argv+1, argc-1))
+			continue;
+
+		if (ce_stage(ce)) {
+			show_unmerge(ce->name);
+			while (i < entries &&
+			       !strcmp(ce->name, active_cache[i]->name))
+				i++;
+			i--; /* compensate for loop control increments */
+			continue;
+		}
+ 
+		if (stat(ce->name, &st) < 0) {
+			if (errno != ENOENT) {
+				perror(ce->name);
+				continue;
+			}	
+			if (silent)
+				continue;
+			show_file('-', ce);
+			continue;
+		}
+		changed = cache_match_stat(ce, &st);
+		if (!changed)
+			continue;
+
+		oldmode = ntohl(ce->ce_mode);
+		mode = S_IFREG | ce_permissions(st.st_mode);
+
+		show_modified(oldmode, mode, ce->sha1, null_sha1,
+			      ce->name);
+	}
+	return 0;
+}