MB-100 Fix compilation with automake 1.13.

AM_CONFIG_HEADER has been obsoleted.

Change-Id: I10590b3a6c98e7d03d95902c1e9f3fd427a1cf3a
Reviewed-on: http://review.couchbase.org/25179
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>