Here is a patch that fixes a serious endless loop problem on 32 bit

architectures near the timestamp 2^31 (oh yes - y2k038 is showing its ugly
face) when using the graph command(s). Once the endtime of a graph is
above the mentioned timestamp, mktime always returns -1 (and correctly
so), causing some loops to loop forever. The patch fixes this, causing
some strange output, but there is no other sane way to handle this (expect
by switching to a 64 bit platform). -- Peter Stamfest

git-svn-id: svn://svn.oetiker.ch/rrdtool/trunk/program@2146 a5681a0c-68f1-0310-ab6d-d61299d08faa