Fix bug 424: doing full_read breaks things like cat which should return a

chunk of data when they get it and not block until they've buffered 4k.

The use case was cat /proc/psaux, but you can also reproduce this by
running non-busybox cat by itself and typing things at the command line.
Then run busybox cat.  Notice how cat is _supposed_ to echo each line back
to us as we hit enter?

libbb/copyfd.c

@@ -33,7 +33,7 @@ static ssize_t bb_full_fd_action(int src_fd, int dst_fd, size_t size)
 	while (!size || total < size)
 	{
 		ssize_t wrote, xread = (size && size < BUFSIZ) ? size : BUFSIZ;
-		xread = bb_full_read(src_fd, buffer, xread);
+		xread = safe_read(src_fd, buffer, xread);
 		if (xread > 0) {
 			/* A -1 dst_fd means we need to fake it... */
 			wrote = (dst_fd < 0) ? xread : bb_full_write(dst_fd, buffer, xread);