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

Change-Id: I624f959229a91329507aec5ff61045c49d296401
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>