Add the "eForce" parameter to the sqlite3_multiplex_shutdown() entry point
in test_multiplex.c.  Shutdown is forced if true.  Shutdown is not done if
there are pending database connections and eForce is false, but an error log
entry is made instead.
Add three new static mutexes for use by the application.  This is a partial
import of changes from the threads branch.
Re-integrate the recent changes from the 'winMutex' branch back into the Win32 mutex subsystem.
Deactivate the DISTINCT in a SELECT on the right-hand side of an IN operator,
since it should not make any difference in the output but dues consume extra
memory and CPU time.
Fix a leaked statement handle in pager2.test.
Add a missing call to "test_sqlite3_log" to multiplex.test.
Optimizations to the OS sub-type checking in the Win32 VFS.
Omit a pointless OP_Null when processing a value-list RHS of an IN operator
where the LHS is a rowid.
Refactoring:  Change "pIndex->onError!=OE_None" to use a macro:
"IsUniqueIndex(pIndex)".  Easier to understand that way.
Enhance the PRAGMA integrity_check command to detect UNIQUE and NOT NULL
constraint violations.
Begin making changes to the IN operator in an attempt to make it run faster
and to make the code easier to understand.
The idea of coding IN operator with a short list on the RHS as an OR expression
turns out to be helpful.  If the list is of length 1 or 2, the OR expression
is very slightly faster, but the ephemeral table approach is clearly better for
all list lengths greater than 2.  Better to keep the code simple.
Clean up the IN operator code generation logic to make it easier to reason
about.  In the process, improve code generation to omit some unused OP_Null
operations.
Remove an unnecessary OP_Null in the IN-operator logic.  Attempt to clarify
comments explaining the IN-operator code, though it is not clear that the
comments are correct even yet - more work to be done.
Improved detection and handling of NULL values on the RHS of a IN operator.
A better comment on the generated code for the NULL-in-RHS-of-IN detection
logic.
Remove (newly) incorrect preprocessor check to fix build on WinRT.
Enhancements to the code generator for the IN operator that result in much
faster queries in some cases, for example when the RHS of the IN operator
changes for each row of a large table scan.
Refinements to the enhanced IN-operator logic.
Further enhancements to IN-operator processing.