Windows: Enforce free space checks every 1MB

Instead of performing a free space (or quota) check on every extending
write, perform the check only when the file length is increased beyond
the next 1MB boundary.   The file server permits 1MB quota over runs
and issuing the volume status rpc to the file server is extremely
expensive.  Especially for append only applications that write just a few
bytes at a time.

Change-Id: I74ff17ba5a95adb41350add24bc09a74c950a4fb
Reviewed-on: http://gerrit.openafs.org/9555
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Revert "Windows: Treat all cached writes as write-through"

This reverts commit 5130681fa2d4a35d3f0b578d92c5db1892fdfb18.

Change-Id: If33a6e1f6969628eaa74d5a56f2eec5560d827f4
Reviewed-on: http://gerrit.openafs.org/9572
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>