This adds an extra option to allow setting the SQLite page cache size as a regular option.
Prior to this commit it was only possible to set the SQLite page cache size via environment variables.
The option to use environment variables is preserved, and as options from the environment variable are applied after the new setting, environment variables take precedence.
The default value for the new option is to use 1% of the system memory for the page cache. For the restore process, a connection per worker may be made which defaults to half the number of cores, so the maximum amount of memory is 1% * half the CPU cores.
This is just the upper limit, and SQLite may choose not to use all of it.
This fixes#6178
This PR adds a few extra consistency checks to the database, so any failure in the operations is detected earlier than before.
Especially when cleaning temporary and partial files, it is important that the deletes do not remove unexpected entries.
Also, after a recreate, repair or purge command, the database consistency is verified, so it becomes easier to identify which operation caused the failure.
To assist in trouble shooting, there is also a more elaborate error message if a fileset discrepancy is detected, that pinpoints which versions are affected.
Finally, the repair command has been extended to support recreating a fileset from the remote data.
Update the SQL to also group on size (just in case).
Renamed the normal read method to signal that it is unverified.
Made the verified reader use enumeration state machine to avoid materializing the list.
`var`-ified some of the test code.
Kenneth Skovhede