dist/: implement warnings-by-default

[jkeenan]

In this ticket we will track our progress on implementing Objective 3, warnings-by-default, for tests in the dist/ directory in the core distribution. See that ticket for guidance on addressing warnings.

On Oct 11 I ran make test on the alpha-dev-03-warnings branch at commit 78482fc. I then chopped up the output into individual files, gzipped them, and placed them for your reference in this directory on my server.

By my count, the line count in the output file was 544, which compares with a line count of 440 for the same group of files when I run make test on the alpha branch at commit c5c5fb4. So one, somewhat crude way of measuring our progress is how far we manage to reduce the line count in these test runs.

Acceptance Criteria: All tests for this subdirectory PASS; no tests emit warnings.

[jkeenan]

Tickets created while working on this ticket:

dist/Data-Dumper/t/dumper.t: fails with warnings on by default
dist/Storable/t/code.t: test failure when run with warnings on by default

[jkeenan]

As of 5dc2ff8, the only test not passing in this subdirectory is dist/Storable/t/code.t. See: #319.