Revert task flag re-ordering, add comments

Roland points out that the flags end up having non-obvious dependencies
elsewhere, so revert aa55a08687059aa169d10a313c41f238c2070488 and add
some comments about why things are as they are.

We'll just have to fix up the broken comparisons. Roland has a patch.

Signed-off-by: Linus Torvalds <torvalds@osdl.org>