to no longer insist that len(seq) be defined.
NEEDS DOC CHANGES.
This is meant to be a model for how other functions of this ilk (max,
filter, etc) can be generalized similarly.  Feel encouraged to grab your
favorite and convert it!
Note some cute consequences:
    list(file) == file.readlines() == list(file.xreadlines())
    list(dict) == dict.keys()
    list(dict.iteritems()) = dict.items()
    list(xrange(i, j, k)) == range(i, j, k)