Windows: Improve logging for StoreMini and cm_BufWrite

Windows: Improve logging for StoreMini and cm_BufWrite

Add trace logging to cm_StoreMini which never had it before.

Improve the logging of cm_BufWrite by adding the trucPos value
which is the new length of the file that is being reported to
the file server.

Remove cm_buf_t data references when cm_BufWrite is performing
operations using rx_Writev and iovec structures.

Change-Id: I28798eb2232e739f665eb51499305a7a1898f824
Reviewed-on: http://gerrit.openafs.org/4924
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>
Tested-by: Jeffrey Altman <jaltman@openafs.org>