pike version numbering

the main reason for that is that if we continue with 7.10, 7.12, etc, we will NEVER reach a state where the changes are large enough to get to pike 8 because after 7.10 and further switching to 8 will create expectations where pike 8 would be significantly different from pike 7.

We have a new compiler in development and we have other things like stable ABI that would warrent a large step forward. We also have some large scale plans for what to do with strings vs. byte sequences and we have the ongoing process of swapping out static and use protected instead. All of this together would probably warrent a step from 7.8 to 8.0 (through the 7.9 development branch).

I do not agree that we should never go to 7.10. I just don't see that as likely.