[texinfo-pretest] the new @quotation command

[Karl Berry]

    And about the other thing I said, that is restrict the first
    argument to be an identifier to be used in a class=""?

If the second arg is present, the first arg could be used as a css class.
If the second arg is not present, I don't think it's worth it.
I hate to change the spec of how the @quotation arg works already.

Also, there has to be some interaction with the CSS for @quotation itself.
Maybe have subclasses or whatever CSS calls it.