Checkblocks now checks the last 2500 blocks by default. On systems with slow disks, this takes in the order of a minute or more. I believe we can safely reduce this number, as the coindb checks are only done to the last ~150 blocks anyway, but they are very thorough. Corruption in blocks further back will at most be a problem for rescanning/reindexing/serving, but has no chain splitting risk.
288 blocks (=2 days) seems a reasonable amount to me.
