switch to hsize_t for hdf5 offset and stride

[kevinhkhuynh]

This is a small bug fix for issue #813.

[cyrush]

thanks @kevinhkhuynh! It looks like there is a python related issue, I'll smooth that out.

[kevinhkhuynh]

thanks @kevinhkhuynh! It looks like there is a python related issue, I'll smooth that out.

Thanks, Cyrus!

[cyrush]

python issue was just that it was expecting an exception for neg numbers, we no longer need that check.

[coveralls]

Coverage increased (+0.07%) to 86.423% when pulling 3998c83 on bugfix/conduit-hdf5-offset into 7e6918c on develop.

[cyrush]

thanks @kevinhkhuynh !