Zodbcommit reads input in zodbdump format from stdin and then uses
zodbdump.DumpReader to parser that input. The parser works on binary
data.

However zodbcommit, was preparing that input data mixing bytes and
strings, which is failing on py3:

    (py3.venv) kirr@deca:~/src/wendelin/z/zodbtools$ zodb commit 1.fs 00
    Ignoring index for /home/kirr/src/wendelin/z/zodbtools/1.fs
    aaa
    Traceback (most recent call last):
      File "/home/kirr/src/wendelin/venv/py3.venv/bin/zodb", line 33, in <module>
        sys.exit(load_entry_point('zodbtools', 'console_scripts', 'zodb')())
      File "/home/kirr/src/wendelin/z/zodbtools/zodbtools/zodb.py", line 129, in main
        return command_module.main(argv)
      File "/home/kirr/src/wendelin/venv/py3.venv/lib/python3.9/site-packages/decorator.py", line 232, in fun
        return caller(func, *(extras + args), **kw)
      File "/home/kirr/src/tools/go/pygolang/golang/__init__.py", line 103, in _
        return f(*argv, **kw)
      File "/home/kirr/src/wendelin/z/zodbtools/zodbtools/zodbcommit.py", line 222, in main
        zin += sys.stdin.read()
    TypeError: can't concat str to bytes

-> Fix it by reading stdin in binary mode.

No test currently as zodbcommit.main is not covered by tests (hopefully yet).