Windows: Release Notes updates

Document ReparsePointPolicy registry value.

Document known Explorer Shell Paste bug.

Update ShortNames registry value.

Document Cygwin 1.7.18-1 support for AFS Symbolic Links.

(cherry picked from commit 79c7b34afd3231a80a7aa4f163b89cb6eca4dfb7)

Change-Id: If01d25937be6a7b0c9db9b6d65f0bcb55ae580b9
Reviewed-on: http://gerrit.openafs.org/9872
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>