Request to increase the size of the SystemRequest structure

[Justin Hibbits]

Been looking at the system interfaces for LSD, and I've concluded  
that there are some system requests, namely commit, that require more  
than 64-bytes to account for both the payload and bookkeeping.  Thus,  
I recommend we increase the length to 128 bytes. I know we have the  
extra payload option, but I'm not certain how much trouble that will  
be.  This method keeps as much inline as possible, and still offers  
32 system requests possible at once, which is far more than can be  
generated at any given time (time slice doesn't really allow for much  
more than 8 requests, from what I can tell, given the speed of an x86  
CPU).

Also, today I came upon an optimization that would would also  
simplify things a great deal, and that requires embedding a function  
callback and arbitrary data (in this case 2 pointers) into the  
request structure (extra payload).

Currently the userspace system is designed only for objective-C,  
which completely removes any chance for using straight C as  
callbacks, unless wrapped in objective-C wrappers.  This optimization  
and simplification is greatly desirable, for James and the system  
runtime environment.

Thoughts?

- Justin