We did not have a safe_write, which is the analog to safe_read. Convert

full_write to use safe_write internally, which is needed to guarantee proper
behavior, i.e. when writing to a pipe.

libbb/full_write.c

@@ -36,7 +36,7 @@ ssize_t bb_full_write(int fd, const void *buf, size_t len)
 	total = 0;
 
 	while (len > 0) {
-		cc = write(fd, buf, len);
+		cc = safe_write(fd, buf, len);
 
 		if (cc < 0)
 			return cc;		/* write() returns -1 on failure. */