Proposal: Test::MakeVariantTestFiles

The DBI adopted an approach towards testing 'variants' by creating extra
test files that act as wrappers around existing test files.

The wrappers modify the process in some way, such as setting environment
variables, before executing the original test file.

It works well, and the DBIT has adopted the same approach.

I think the approach is good and more widely applicable than just the DBI.

I'd like to propose that we factor it out into a separate distribution.

Thoughts?

Tim.