turn on stack zeroing for addronly leak detection

_From [bruen...@google.com](https://code.google.com/u/109494838902877177630/) on October 12, 2011 18:10:55_

no-uninits mode has no definedness info for FPO cstacks or for leaks:
perhaps should auto-turn-on stack zeroing like for -leaks_only.
I've already hit a false negative where a leak is missed in my new test for issue #533 .

should also update the docs to recommend disabling FPO for this mode
(I already updated http://dev.chromium.org/developers/how-tos/using-drmemory )

_Original issue: http://code.google.com/p/drmemory/issues/detail?id=624_