Test for ExaminePage, fix two bugs it found.

This constructs `/contigs`, `/spec` and `/genotypes` responses from a VCF file.

The two bugs were:

  1. The initial request for `/genotypes` was being throttled, which artificially slowed page load by 500ms.
  1. The exploded rows from multiple samples were being dropped.

I also deleted some code that wasn't being used to boost our code coverage. I suspect that if/when we revive this code, it will be substantially different. So deleting is not a big loss. But feel free to disagree.

This PR bumps our test coverage from 25%→[53%](https://coveralls.io/r/hammerlab/cycledash).
Better to wrap in Error(…) so all JS runtimes can package the stacktrace etc