VCF sorting change breaks existing VCFs

[lbergelson]

I failed to consider the effect of changing the VCF sort order on processing existing VCFs when merging https://github.com/samtools/htsjdk/pull/1593. This breaks many things.

I think this is still a good idea but we need to reconsider how to do it safely, possibly a split comparator with different levels of sorting vs validating like the sam sort orders use.

The commit e2943b78ff595e144281b8a3c126be5a4d70085d reverts https://github.com/samtools/htsjdk/pull/1593.

This blocks https://github.com/samtools/htsjdk/pull/1629 as well.

[lbergelson]

@clintval Sorry, I rolled your change back for now. I'd like to get it back in but it might take me a bit to get to it.