The open opcode

[Allison Randal]

Andrew Whitworth wrote:
> In the case of the open operation, avoiding the PCC call is probably
> not a huge savings. Open is not called often enough to make a huge
> difference either way. Operations like read/write are both called far
> more often so the saves there really do add up over time. I have no
> problem making the uncommon case more expensive if it gives us better
> security utility. I'm sure we could find performance savings elsewhere
> in the IO subsystem to make up for it.

A method call isn't what's needed here anyway. All it needs is to look 
up the FileHandle class from the namespace instead of instantiating it 
from the type id.

Allison