The GATK command line header keys were being repeated in the VCF and
subsequently lost to a single key value by HTSJDK. This resolves
the issue by appending the name of the walker after the text
"GATKCommandLine" and a number after that if the same walker was
used more than once in the form: GATKCommandLine.(walker name) for
the first occurrence of the walker, and GATKCommandLine.(walker name).#
where # is the number of the occurrence of the walker (e.g.
GATKCommandLine.SomeWalker.2 for the second occurrence of SomeWalker).
Integration test added to EngineFeaturesIntegrationTest to verify
two runs of same walker follow expected form.
Resolves#909
See also: HTSJDK #43
024ec69e97