vlserver - Don't overflow buffer with backup pattern

vlserver - Don't overflow buffer with backup pattern

based on a report from Hans-Werner Paulsen

avoid adding regex anchors to a buffer which is already full
when copying it to a like sized buffer. instead, leave extra space.

Change-Id: I486c51779da285888fe38ed2aa5f30dd2d008a9a
Reviewed-on: http://gerrit.openafs.org/2456
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Tested-by: Derrick Brashear <shadow@dementia.org>
Reviewed-by: Derrick Brashear <shadow@dementia.org>