vcfdistance: Correctly handle various edge cases
vcfdistance: Correctly handle various edge cases

Tests added in previous commit now pass.

Diff best viewed with whitespace ignored.

tomdcsmith/vcflib,vcflib/vcflib,harshinamdar/vcflib,harshinamdar/vcflib,zhmz90/vcflib,harshinamdar/vcflib,zhmz90/vcflib,glennhickey/vcflib,vcflib/vcflib,zhmz90/vcflib,ekg/vcflib,vcflib/vcflib,harshinamdar/vcflib,glennhickey/vcflib,wzugang/vcflib,travc/vcflib,wzugang/vcflib,wzugang/vcflib,vcflib/vcflib,ashishjain1988/vcflib,harshinamdar/vcflib,wzugang/vcflib,zhmz90/vcflib,ekg/vcflib,harshinamdar/vcflib,ashishjain1988/vcflib,vcflib/vcflib,vcflib/vcflib,ekg/vcflib,glennhickey/vcflib,vcflib/vcflib,vcflib/vcflib,tomdcsmith/vcflib,ashishjain1988/vcflib,zhmz90/vcflib,ashishjain1988/vcflib,glennhickey/vcflib,tomdcsmith/vcflib,zhmz90/vcflib,ekg/vcflib,travc/vcflib,ashishjain1988/vcflib,travc/vcflib,glennhickey/vcflib,wzugang/vcflib,glennhickey/vcflib,ashishjain1988/vcflib,ekg/vcflib,wzugang/vcflib