Avoid a (harmless) buffer overread that is possible on an OOM when
MEMSYS5 is engaged.
In the command-line shell, run set writable_schema before running the
".clone" command.
Fix minor errors causing compilation to fail with SQLITE_MAX_WORKER_THREADS set to a value greater than zero.
Fix a typo in the "Synopsis:" comment for the OP_VFilter opcode.
Fix an integer overflow problem in the sorter.
Use OP_Copy instead of OP_SCopy when moving results out of a subquery,
to prevent the subquery results from changing out from under the outer
query.  Fix for ticket [1e64dd782a126f48d78].
Merge all recent changes from trunk.
Change vdbeSorterExtendFile() so that it makes a best effort to create the
PMA file of the desired size, but does not return an error if unable.
Add test file sort3.test, which should have been part of commit [9d3351b8d7].