Attempt #2 stopping test erosion

[kentfredric]

This is mostly a rehash of #19 aiming to simplify the situation, and remove swathes of contemptuos code.

The biggest downside now from this test is that it doesn't have the Test::TempDir::Tiny magic that shits stuff in ./tmp/ with a pretty path name.

Instead, something as effective, but much simpler is used:

• We use a regular tempdir
• We have an ENV flag that stops it being reaped entirely
• And we just "note" the path to it.

Its not as "nice"... but probably sufficient.

All the faff in my other PR has been basically inlined where needed.

HOWEVER

Both in this test iteration, and the one before it, doing:

perl -Ilib t/maniskip-include-default.t

Fails test 2:

not ok 2 - Makefile still skipped by default
#   Failed test 'Makefile still skipped by default'
#   at t/maniskip-include-default.t line 37.

Whereas that test does not fail without -Ilib.

But the tests pass properly with dzil test

Somebody needs to investigate what the fuck is happening here.

Included file "lib/ExtUtils/MANIFEST.SKIP" not found - skipping at lib/ExtUtils/Manifest.pm line 495, <M> line 1.

That looks like some funky fragile logic happening.

[haarg]

The default MANIFEST.SKIP file is found based on the path to the ExtUtils::Manifest module. If you load the file from a relative path, but change directory, it won't be able to find it. The path should probably be converted to absolute at load time. This is unrelated to the include_default change.