Back-port changes of Jan 16 and 17 to "revoke" pending fsync requests during

Back-port changes of Jan 16 and 17 to "revoke" pending fsync requests during
DROP TABLE and DROP DATABASE.  Should prevent unexpected "permission denied"
failures on Windows, and is cleaner on other platforms too since we no longer
have to take it on faith that ENOENT is okay during an fsync attempt.

Patched as far back as 8.1; per recent discussion I think we are not going
to worry about Windows-specific issues in 8.0 anymore.