used for new area.
MemPool::AddToPool() now gracefully deals with NULL pointers (or a size of 0).
BitmapManager was deleting the area it transferred to AreaPool before - it
no longer needs an extra area, though.
Minor other cleanup.
git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@13260 a95241bf-73f2-0310-859d-f6bbb57e9c96