Don't use implicit conversions to c_int, which incidentally happen to work
on (some) 64-bit platforms, but:
* may lead to truncation of the input value to a 32-bit signed int,
* cause segfaults on some 32-bit architectures (tested on Ubuntu ARM,
but is also the likely cause of issue #1707).
Also, when passing references use explicit 64-bit integers, where needed,
instead of c_ulong, which is not guaranteed to be this large.
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