device_memory_interface::space() assert against NULL and
return a reference, and pushed references throughout all
address space usage in the system. Added a has_space()
method to check for those rare case when it is ambiguous.
[Aaron Giles]
Also reinstated the generic space and added fatal error
handlers if anyone tries to actually read/write from it.
read/write handlers to take an address_space & instead
of an address_space *. Also update pretty much all other
functions to take a reference where appropriate.
[Aaron Giles]
