The data in the tree test cannot be automatically converted to `bytes`
as a encoding is necessary in that case:

```python
Traceback (most recent call last):
  File "/srv/slapgrid/slappart66/git/pygolang/golang/__init__.py", line 125, in _
    return f(*argv, **kw)
  File "/srv/slapgrid/slappart66/git/wendelin.core/wcfs/internal/xbtree/xbtreetest/treegen.py", line 281, in TreesSrv
    zblk.setblkdata(v2)
  File "/srv/slapgrid/slappart66/git/wendelin.core/bigfile/file_zodb.py", line 294, in setblkdata
    blkdata = bytes(buf)                    # FIXME does memcpy
TypeError: string argument without an encoding
```

As we know that the data is ASCII, we use the ASCII encoder to convert
it to `bytes`.