r20918: a bit more debugging, and remove the hackish /dev/null writes I used

r20918: a bit more debugging, and remove the hackish /dev/null writes I used
to track down some uninitialised memory (sometimes valgrind gets the
offset wrong, writing to /dev/null 1 byte at a time avoids this)
(This used to be commit 4bf741b567417231c29606904aea2af0a91c941c)