Windows: Check Avail Space on extending SetEndOfFile

Windows: Check Avail Space on extending SetEndOfFile

When cm_SetLength() is called with an extending file length,
check the available free space in the volume to see if the
new length will fit.  If not, return CM_ERROR_SPACE.

This permits applications to discover that there is insufficient
space prior to writing all of the data into the windows page
cache at which point it will be too late.

There is still the possibility of a race that can result in
data loss if two applications are writing into the same volume
at the same time and there is insufficient room.

Change-Id: Ieef2c48f5b6edc8d101b6527af3a3f87fe55f6ca
Reviewed-on: http://gerrit.openafs.org/7057
Tested-by: Jeffrey Altman <jaltman@secure-endpoints.com>
Reviewed-by: Jeffrey Altman <jaltman@secure-endpoints.com>