ENH: add a ndarray super-fast path to _array_from_object

When the argument is exactly an ndarray and the rest of the arguments
are their defaults we can skip the very slow
PyArg_ParseTupleAndKeywords.
This improves np.array(ndarray, copy=False) performance by about a
factor three and np.asarray(ndarray) by about a factor of two.

also add some interned strings to multiarraymodule
OK, I see this branches to `full_path` often.