Windows: afs_shl_ext improve overlay handlers

Windows: afs_shl_ext improve overlay handlers

Add link.ico and mount.ico Windows icon files.
Use these images as overlays instead of extracting an image
from shell32.dll which is a bad idea.  See

http://blogs.msdn.com/b/oldnewthing/archive/2005/10/26/485133.aspx
Reviewed-on: http://gerrit.openafs.org/3445
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Tested-by: Stefan Kueng <tortoisesvn@gmail.com>
Reviewed-by: Stefan Kueng <tortoisesvn@gmail.com>
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>
Tested-by: Jeffrey Altman <jaltman@openafs.org>
(cherry picked from commit 3ff9c24c0e2d72dcce65fc7706dcdb1cd3090965)

Change-Id: Ifa20508a1b30ebd88e4968d76d325c2e2be51039
Reviewed-on: http://gerrit.openafs.org/3786
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>