Iterate PyObject without conversion

[jw3126]

I am in a situation, where I want to iterate over a PyObject, without converting the items into julia objects.
My quick and dirty solution was to copy the iterate code and remove the conversion here:

PyCall.jl/src/pyiterator.jl

Line 37 in ae9bbba

return (convert(PyAny, s[1]), (nxt, s[2]))

Is there a better way? Would you like a PR that adds a lower level function without conversion (say pyiterate) and makes iterate a stub that just adds convert on top of this function?

[tkf]

a dup of #153
see also #507

[tkf]

closed by #594 (thanks!)