A couple of changes in various interrupt and thread functions and structures.
These make it now possible to change the stack at any time without making the kernel crash. This is needed for calling VESA 3.0 VBE functions through the protected mode interface.
git-svn-id: file:///srv/svn/repos/haiku/trunk/current@422 a95241bf-73f2-0310-859d-f6bbb57e9c96
