Windows: Insert Server Reference List changes

Windows: Insert Server Reference List changes

When inserting a new cm_serverRef_t object into a server list
perform the following operations:

1. take advantage of the fact that the cm_serverLock is held
   exclusively to purge the list of any deleted entries that
   could not be removed previously.

2. check to ensure that the item that is being added does not
   already exist in the list.  If it does, discard it.

Reviewed-on: http://gerrit.openafs.org/5258
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Tested-by: Jeffrey Altman <jaltman@openafs.org>
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>
Reviewed-by: Derrick Brashear <shadow@dementix.org>
(cherry picked from commit 5b40c5f5294964fc09df2c8332ab63cd2d729264)

Change-Id: I94398476267dda82e82306a87aa0bba6aa41da00
Reviewed-on: http://gerrit.openafs.org/5264
Reviewed-by: Derrick Brashear <shadow@dementix.org>
Tested-by: Derrick Brashear <shadow@dementix.org>