* Fault only happens if labs(year) > INT_MAX/dpy!

The current code has a potential problem when checksums are computed
for objects larger than 32bit allows for.

* The corresponding faults only happen when reshReplace results in a
  non-contiguous list or a non-contiguous list is extended.

* Fixes an implicit conversion.

* The actual value is only relevant when ioMode != PIO_NONE.

Fail early instead.

Fail early instead.

Fail early instead.

Fail early instead.

Fail early instead.