fix bug in caching chart: We USED TO chart the value of max-age (including "null" === "there is no max-age"). NOW we chart the "freshness lifetime" which includes max-age and Expires, plus looking at no-store and no-cache. So "null" is now included in "t = 0".
fix bug in caching chart: We USED TO chart the value of max-age (including "null" === "there is no max-age"). NOW we chart the "freshness lifetime" which includes max-age and Expires, plus looking at no-store and no-cache. So "null" is now included in "t = 0".

git-svn-id: d5a8a4092b1c3eddbe100e0c5fc6446cfb12afd1@1111 fc7d47d3-c008-acd5-f51f-d19787b8a02f

HTTPArchive/httparchive,HTTPArchive/httparchive,paulcalvano/httparchive,paulcalvano/httparchive