Flatten tools/ directory to make build procedure simpler.

Also make platform specific part more isolated.  Currently we only
have Darwin defined, but I've taken a look at SunOS specific patch
(which I dropped on the floor for now) as well.  Doing things this way
would make adding it easier.

Signed-off-by: Junio C Hamano <junkio@cox.net>

mailsplit.c

@@ -0,0 +1,145 @@
+/*
+ * Totally braindamaged mbox splitter program.
+ *
+ * It just splits a mbox into a list of files: "0001" "0002" ..
+ * so you can process them further from there.
+ */
+#include <unistd.h>
+#include <stdlib.h>
+#include <fcntl.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <sys/mman.h>
+#include <string.h>
+#include <stdio.h>
+#include <ctype.h>
+#include <assert.h>
+
+static int usage(void)
+{
+	fprintf(stderr, "mailsplit <mbox> <directory>\n");
+	exit(1);
+}
+
+static int linelen(const char *map, unsigned long size)
+{
+	int len = 0, c;
+
+	do {
+		c = *map;
+		map++;
+		size--;
+		len++;
+	} while (size && c != '\n');
+	return len;
+}
+
+static int is_from_line(const char *line, int len)
+{
+	const char *colon;
+
+	if (len < 20 || memcmp("From ", line, 5))
+		return 0;
+
+	colon = line + len - 2;
+	line += 5;
+	for (;;) {
+		if (colon < line)
+			return 0;
+		if (*--colon == ':')
+			break;
+	}
+
+	if (!isdigit(colon[-4]) ||
+	    !isdigit(colon[-2]) ||
+	    !isdigit(colon[-1]) ||
+	    !isdigit(colon[ 1]) ||
+	    !isdigit(colon[ 2]))
+		return 0;
+
+	/* year */
+	if (strtol(colon+3, NULL, 10) <= 90)
+		return 0;
+
+	/* Ok, close enough */
+	return 1;
+}
+
+static int parse_email(const void *map, unsigned long size)
+{
+	unsigned long offset;
+
+	if (size < 6 || memcmp("From ", map, 5))
+		goto corrupt;
+
+	/* Make sure we don't trigger on this first line */
+	map++; size--; offset=1;
+
+	/*
+	 * Search for a line beginning with "From ", and 
+	 * having something that looks like a date format.
+	 */
+	do {
+		int len = linelen(map, size);
+		if (is_from_line(map, len))
+			return offset;
+		map += len;
+		size -= len;
+		offset += len;
+	} while (size);
+	return offset;
+
+corrupt:
+	fprintf(stderr, "corrupt mailbox\n");
+	exit(1);
+}
+
+int main(int argc, char **argv)
+{
+	int fd, nr;
+	struct stat st;
+	unsigned long size;
+	void *map;
+
+	if (argc != 3)
+		usage();
+	fd = open(argv[1], O_RDONLY);
+	if (fd < 0) {
+		perror(argv[1]);
+		exit(1);
+	}
+	if (chdir(argv[2]) < 0)
+		usage();
+	if (fstat(fd, &st) < 0) {
+		perror("stat");
+		exit(1);
+	}
+	size = st.st_size;
+	map = mmap(NULL, size, PROT_READ, MAP_PRIVATE, fd, 0);
+	if (map == MAP_FAILED) {
+		perror("mmap");
+		close(fd);
+		exit(1);
+	}
+	close(fd);
+	nr = 0;
+	do {
+		char name[10];
+		unsigned long len = parse_email(map, size);
+		assert(len <= size);
+		sprintf(name, "%04d", ++nr);
+		fd = open(name, O_WRONLY | O_CREAT | O_EXCL, 0600);
+		if (fd < 0) {
+			perror(name);
+			exit(1);
+		}
+		if (write(fd, map, len) != len) {
+			perror("write");
+			exit(1);
+		}
+		close(fd);
+		map += len;
+		size -= len;
+	} while (size > 0);
+	return 0;
+}