among other things, this allowed to remove around a thousand of machine() parameters
passed to re-get the state class at each bankswitch operation. readability says thanks.
eventually, nes_mmc and its pieces (nes_pcb, nes_ines & nes_unif) will contain a cart slot device and allow for
things like on-cart sound chips and eeprom devices to be properly emulated
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]
