Be more precise in exception test; move logic to lib

Move the overriding of the Test::Builder functions to a lib for reuse
and be much more explicit about what we expect to occur.
Add a test for aggregating a script that skips to the end
Don't diagnose undef as error, let subtest() do that

See code comments.
Test how 'skip to end' is handled by Nested

Print a warning (including $!) if undef, nothing otherwise
since skip(1) counts as a test and satisfies subtest().
Test how classes handle a read failure
Bump version
UPDATE THE MANIFEST!
Update change log
Ensure test accuracy by requiring diags to match
Explicitly check if tests have run before printing warning

If any tests have been run we can assume the file completed.
Compare read failure to skip (which counts as a test)
Test our usage of Test::Builder to count tests
Update release date in change log