Format-independent templates

This commit series provides a generalized facility to make any template set independent of package format. For t/tests, watch files that are not needed for native packages are removed. Unlike the previous implementation, it now happens early in the provisioning process before the test specification is copied into the work directory. For details, please see the commit messages.

The series is bundled with modifications to three tests that served as the inspiration for the new mechanism. They also show that it works.