type safe Machine IL, code generator, and runtime

[Stephen Weeks]

> Speaking  of checking limit checks, when I was trying to trace down the bug I
> tried to figure out if we could check (in  a  debug  version)  if  the  limit
> checks  were  correct  in  the  following way: at every check, you record the
> amount checked for and the current frontier.  Before that  you  look  at  the
> current  frontier  and  compare  it  to the previous checks frontier + amount
> previously checked for.  If the frontier is farther  then  there  is  a  bug.
> This gets slightly more complicated because of the amount of space guarenteed
> to be there, but seems do-able.

Easy enough in the C backend by modifying some macros.  Go for it.