Convert to using Test::More. Provide each test with a description.

For: RT #120503.  This entailed:

Replacing each instance of Check() and CheckDie() with appropriate
Test::More functions.

Replacing MkDir() and touch() with mkdir_ok() and create_file_ok() to
create a more Test::More-ish interface; create symlink_ok() to handle
similar circumstances.

Providing those three wrapper subroutines with default descriptions,
but allowing a custom description to be passed as an argument.

Highlighting more important unit tests found at the end of subsections
and blocks by prepending 'COMPLETE:' to their descriptions.

More inline comments to guide future maintainers.

Some repositioning of code in order to narrow the scope of variables.
Replacement of hard tabs with spaces; some regularization of indents
and other code tidying.

No tests were added or removed, so the planned number of tests on a
given platform will be unchanged.

TODO:

Some descriptions still need improvement.

There are quite a few File-Find features mentioned in the POD which
are not referenced at all in this test file.  They need to have new
tests written for them.

Coverage analysis.