Fix freopen so it resets stream buffer (#61)

libc/stdio/freopen.c

@@ -46,6 +46,8 @@ FILE *freopen(const char *pathname, const char *mode, FILE *stream) {
       dup3(fd, stream->fd, flags & O_CLOEXEC);
       close(fd);
       stream->iomode = flags;
+      stream->beg = 0;
+      stream->end = 0;
       return stream;
     } else {
       return NULL;