MB-100 Fix compilation with automake 1.13.

AM_CONFIG_HEADER has been obsoleted.

Change-Id: I21ea9680982f40405c50ffb5fbd3696640582946
Reviewed-on: http://review.couchbase.org/25178
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Reviewed-by: Michael Wiederhold <mike@couchbase.com>