vcftools dependencies: tabix and bgzip

It seems like the tools in the vcftools collection require both bgzip and tabix (see e.g. https://github.com/galaxyproject/tools-devteam/blob/master/tool_collections/vcftools/vcftools_subset/vcftools_subset.xml). However, they are not installed as a dependency from the ToolShed. Are these tools that should be installed on the galaxy user's path, or is this simply a dependency oversight?

Start by reviewing tool_collections/vcftools/vcftools_subset/vcftools_subset.xml and the ToolShed dependency conventions for vcftools. Confirm whether tabix and bgzip must be declared as dependencies or supplied on the Galaxy user's PATH; done means the installation requirement is resolved or clearly documented.

Written by the indexing model from the issue text.