Enhancement: Add more block-comment related tests

My assumption that the final trailing space is not required for single-line block-comments was wrong. Therefore I didn't tweak anything in `nodes.js`. :flushed: 

Nevertheless, I'd still like to add some additional tests, one for single-line block-comments ensuring that the rendering does not change and three more tests related to [jsdoc](http://usejsdoc.org/about-getting-started.html)-like `@doctag`-comments. I also added additional comments to these tests, to emphasize that this pull-request is not yet the final solution. I know this caused lot's of headache for many people and this pull-request will certainly enhance the situation. But it does not solve the issues related to the comment placement, if several variables to comment are involved. I assume this is also the reason why this well known issue is not yet resolved.

Finally I'll also update my [comment](https://github.com/jashkenas/coffee-script/pull/3132#issuecomment-24589102), to clarify that my _“needless additional space in single-line block-comments”_ assumption is wrong.

Good job :smirk: