Null bytes
==========
Reported in https://github.com/andreasvc/pyre2/issues/56

    >>> import re2
    >>> re2.set_fallback_notification(re2.FALLBACK_EXCEPTION)

Using split:

	>>> regex = re2.compile(b",")
	>>> regex.split(b"_first,_\x00second")
	[b'_first', b'_\x00second']

Using sub with a string and count parameter:

	>>> regex = re2.compile(",")
	>>> regex.sub(repl=".", string="_first,_second,\x00third", count=2)
	'_first._second.\x00third'

Using sub with a function as repl:

	>>> regex = re2.compile(",")
	>>> def f(m): return '.'
	>>> regex.sub(repl=f, string="_first,_second,\x00third")
	'_first._second.\x00third'
