Have calls to the xFilter() method of rtree virtual tables ensure that cursor is initialized before proceeding. Fix for [d2889096e7bdeac].
Add the SQLITE_TESTCTRL_ISINIT file control.
Merge the R-Tree fix and the new SQLITE_TESTCTRL_ISINIT test control from
trunk.
Fix the threads build on Windows when SQLITE_MAX_WORKER_THREADS is greater
than 0.
Make the Win32 thread handles are available after the threads exit.
Fix a harmless compiler warning.
Fix unreachable branches in the threads.c module.
Add a couple more assert statements.
Update return value checking to conform to the beginthreadex() specs.
Disable an assert that is sometimes generated spuriously.