Align buffers on HP-UX systems (thanks to Yury Alioshinov)

Change-Id: I1d313cfce4126f53791de504f4240d68ba4263ae
Reviewed-on: http://review.couchbase.org/24502
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Reviewed-by: Yury Alioshinov <haster2010@gmail.com>
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>