* Allow packages to add a 'submodules' property that determines when ad-hoc Git-commit-based versions should initialize submodules
* add support for ad-hoc git-commit-based versions to instantiate submodules if the associated package has a 'submodules' property and it indicates this should happen for the associated spec
* allow Package-level submodule request to influence all explicitly-defined version() in the Package
* skip test on windows which fails because of long paths
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