a rough spot

There are now two bugs causing database corruption. One occurs when doing debugging, the other occurs when the backlinks table splits. And as the code stands, these are not easy bugs to find.

Database integrity is validated by a separate utility and can not currently be called as needed while processing a transaction. But the logic which manages disk space can be enhanced so we can check db integrity at any time--so long as only one thread is running. Seems to me like a very worthwhile project.