Previously, if a SNP occurred in sample A at a position that was in the middle of a deletion for sample B,
sample B would be genotyped as homozygous reference there (but it's NOT reference - there's a deletion).
Now, sample B is genotyped as having a symbolic DEL allele.
Minor cleanup added. Note that I also removed Laura's previous fix for this problem.
Existing integration tests change because I've added a new header line to the VCF being output.
I also added several tests for the new functionality showing:
1. genotyping from separate and already combined gvcfs give the same output
2. genotyping over multiple spanning deletions works
3. combining works too
Existing unit tests also cover this case.
530e0e5ea6