VerifyDelete: Wrap at 78 columns, change messages where they are not making sense.
Constified VerifyDelete().
Remove dangerous (truncation possible) internal path copying.

It was added in commit 4a6fad4993abf03877870c3aa42272444d9511b3
supposedly to fix basedir deletion, but the bug report (Mantis#104)
proved to be bogus and I don't see how this commit has any effect.
Turned comment into debug message.
VerifyDelete(): No change in logic, just restyle

This way it is clear that PROMISE_RESULT is not affected by any prior
state.
Redmine#6331: Skip non-empty directories silently when recursively deleting.
Acceptance tests for file deletions.
Merge pull request #2048 from jimis/redmine6331-delete_tidy_noise

Redmine#6331: Skip non-empty directories silently when recursively deleting