this will fail if strtoll is not available, which is allegedly the case on windows.
it would be better to use PyLong_FromString assuming we have the GIL in this function

there is also duplicate of the bug somewhere in the tracker

there seems to be _strtoi64, _strtoui64 on windows, no idea which version of VS it requires

I wonder if this behavior is correct:

>>> numpy.fromstring('18446744073709551616', sep=' ', dtype='uint64')
array([18446744073709551615], dtype=uint64)
>>> numpy.fromstring('-18446744073709551616', sep=' ', dtype='uint64')
array([0], dtype=uint64)

Shouldn't overflow/underflow generate at least a warning?

yes if its possible via the api it should at least warn, maybe even an error as this is not a computation but IO

I'll take this over, might be useful for 1.9

see #4712
I haven't added overflow handling which is probably useful if you still want to have a go at it.