Error bars with IndexError Bug

[pcwysoc]

Describe the bug
In objectivefns.py, the function _hessian_from_block generates 'firsts' as a tuple, not a list, which causes lines 4730-4731 to experience an IndexError ('too many indices for array: array is 1-dimensional, but 2 were indexed'.

dprobs12_omitted_coeffs = -self.raw_objfn.zero_freq_hterms(total_counts[firsts], omitted_probs)
hprobs_omitted_coeffs = -self.raw_objfn.zero_freq_dterms(total_counts[firsts], omitted_probs)

To Reproduce
I ran into this when loading a dataset from file and then trying to do GST error bars.

Expected behavior
I think we can fix this by adding firsts=list(firsts) on 4719.