Remove an unused variable from the VDBE_PROFILE compile-time option.  Keep the
opcode count in an u32 instead of an int.
In memsys5, initialize new allocations to non-zero bytes.  Change the content
of freed allocations to prevent use after free.  These changes in SQLITE_DEBUG
only.
Close some stray connections in walro.test.
Enhance testing support for the Win32 VFS dynamic extension loading facilities.
Fix several small style/consistency issues with the previous check-in.