Genie:  Move dispatcher et al into namespace relix

Metrowerks C++'s built-in assembler can't deal with symbols from another
namespace, so the kernel boundary functions and the system call registry
(used by the syscall dispatchers) and the 68K hardware exception handler
(which uses the syscall dispatcher) all have to be moved simultaneously.

(Apple's GCC patch for asm {} blocks has no such problem.)
Genie:  Downgrade api/breathe.hh include to relix
relix:  Move deliver_fatal_signal.hh to relix/api

This is a prerequisite of moving deliver_fatal_signal() into MacRelixLib
from Genie, due to interdependency issues.
Genie -> relix:  Factor out check_stack_space()
Genie -> relix:  Move {enter,leave}_system_call()
Merge branch 'move-enter-leave'
Genie:  Make registry iterators local

Fortunately, the vector never changed after LookUpSystemCallByName() was
called, but this is quite wrong.
Genie:  Rename syscall registry symbols
Genie:  Rewrite LookUpSystemCallByName()
Genie -> relix:  Move syscall registration
Genie:  Downgrade SystemCallRegistry.hh dependency
Merge branch 'move-syscall-registry'