sfork(2) now calls sforkr(2) with the current registers.
This will prove useful in creating threads, where user-space now can fully
control what state the child will start in. This is unlike the Linux clone
system call that accepts a pointer to the child stack; this is more powerful
and somehow simpler. Note that this will create a rather raw thread; no
thread initization has been done by the standard thread API (when it is
implemented), so this feature shouldn't be used by programmers unless they
know what they are doing.
fork(2) now calls sfork(2) directly. Also removed fork(2) and sfork(2) from
the kernel as they are done using sforkr(2) now. So technically they aren't
system calls right now, but that could always change.
