Ignore files generated by automake 1.13

Change-Id: Ia07e5fe3eb4bde788850002a0930fbc74db85fbd
Reviewed-on: http://review.couchbase.org/24243
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>