touchup layer buffer-size doc as per change made in mapnik 2.2 (https://github.com/mapnik/mapnik/pull/1566)
touchup layer buffer-size doc as per change made in mapnik 2.2 (https://github.com/mapnik/mapnik/pull/1566)

mapnik/mapnik-reference,mojodna/mapnik-reference,CartoDB/mapnik-reference,gravitystorm/mapnik-reference,gravitystorm/mapnik-reference,mojodna/mapnik-reference,mapycz/mapnik-reference,florianf/mapnik-reference,mapycz/mapnik-reference,mapnik/mapnik-reference,florianf/mapnik-reference,mapnik/mapnik-reference,CartoDB/mapnik-reference