Windows: Avoid unnecessary DNS lookups

Windows: Avoid unnecessary DNS lookups

Windows will attempt to open connections to a broad
range of pipe service (share) names which do not contain
a dot in them.  Attempts to search for these names as
cell names in DNS result in timeouts and sluggish behavior
when browsing \\AFS in the Explorer Shell.

To avoid this problem, do not perform a DNS lookup for a
cellname that doesn't not contain a dot in it.

LICENSE MIT

Reviewed-on: http://gerrit.openafs.org/302
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>
Tested-by: Jeffrey Altman <jaltman@openafs.org>