add make clean step, clean up comments
add make clean step, clean up comments

Change-Id: Icd98da6f5ebaa0f7c7a32135d931cb672e35d5e1
Reviewed-on: http://review.couchbase.org/15060
Reviewed-by: Jan Lehnardt <14e793d896ddc8ca6911747228e86464cf420065@couchbase.com>
Tested-by: Jan Lehnardt <14e793d896ddc8ca6911747228e86464cf420065@couchbase.com>

couchbase/php-ext-couchbase,couchbase/php-ext-couchbase,couchbase/php-ext-couchbase,couchbase/php-ext-couchbase,couchbase/php-ext-couchbase