mmap no longer allows resizing if the object has buffer exports. For example:

    >>> m = mmap.mmap(-1, 4096, access=mmap.ACCESS_WRITE)
    >>> p = (ctypes.c_char * 4096).from_buffer(m)
    >>> m.resize(8192)
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    BufferError: mmap can't resize with extant buffers exported.

    >>> del p
    >>> m.resize(8192)
    >>> len(m)
    8192