Generate a random cur_row for each RRA during

Generate a random cur_row for each RRA during
create/restore operations. This effectively randomizes the block crossings
among RRDs created around the same time. Previously, RRDs that were
created/restored en masse would cross block boundaries simultaneously, which
is sub-optimal.

Also, this patch enables the user to see the RRA's cur_row pointer via
rrdinfo. This was useful during debugging.

-- kevin brintnall kbrint qwest.net

git-svn-id: svn://svn.oetiker.ch/rrdtool/trunk/program@1290 a5681a0c-68f1-0310-ab6d-d61299d08faa