make server->curhost a pointer

This wastes 1k of memory within the server structure and it's barely
ever accessed.

Change-Id: I6db4676138e810e8890f3a1b40b0be800811e26c
Reviewed-on: http://review.couchbase.org/38348
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Brett Lawson <brett19@gmail.com>