0.005 01 fixes

This fixes some oversights/bugs introduced in 0.005_01.  Making this a PR for visibility, but will merge immediately.

Two bug fixes / oversights that I introduced in 0.005_01:

 1. accidentally left a print debug with a YAML dep
 2. one of the skip plans in `t/inline_cpp.t` really needed to be in a `BEGIN` block.

One feature which I believe to be uncontroversial:

 1. add a `t/01_diag.t` that prints out the versions of various required and optional modules

I find this pretty useful when debugging cpan tester reports.  Although some of the versions are provided by cpantesters, some are not.  Or they could be misreporting.  If anyone is concerned about this we can discuss and possible modify/remove for the 0.006 release, but as I say I believe this to be uncontroversial.