added screed and read_parser streaming testing

Marked as known failing since they currently fail.
Will investigate.

Relevant to #393, #654
Mmh, here I think

    if S_ISBLK(mode) != 0:

is unambiguously clearer than

    if not S_ISBLK(mode) == 0:

You could alternatively do:

    if S_ISBLK(mode):

which is probably cleanest, unless you're trying to make a point (which I don't think is the case).