Fix memory/resource leaks for WinCE and Cygwin.
Fix memory and resource leaks for WinCE and Cygwin, and a compiler warning
on windows with SQLITE_THREADSAFE=0.
Clear a valgrind error by zeroing the first 4 bytes of the temp-space allocation used by the b-tree module.
Fix a typo in a requirements mark comment.  No changes to code.