packagefs: AttributeIndex: Support duplicates correctly

The tree comparisons didn't allow for different Nodes having the same
attribute value. Therefore only the first node would be added and later
we would try to remove a node not actually in the tree, leading to a
crash.

packagefs seems to finally unmount cleanly, now.
VM: Fix vm_block_address_range() area protection

B_ALREADY_WIRED, which was erroneously passed for the area protection
parameter to map_backing_store(), has the value 7 which implies user
readable and writable. Hence the address ranges around 0xdeadbeef and
0xcccccccc could actually be read and written from anywhere.