condensed rewrite chapter 6.2 Versioning

Weeded out a possible contradiction where one might understand that all
versions prior to 1.0 are considered incompatible, but there was also a
note on preserving backward compatibility with 0.95.

If the requirement is to reject every request prior to 1.0, (see second paragraph in the upstream master chapter 6.2) the note becomes irrelevant. I suggest leaving it out until the first version of the spec AFTER 1.0 is released, introducing situations of valid version differences.