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_DEVICE*_HANDLERs are now passed an
address_space &, and the 8-bit variants get a mem_mask
as well. This means they are now directly compatible
with the member function delegates. Added a generic
address space to the driver_device that can be used
when no specific address space is available. Also
added DECLARE_READ/WRITE_DEVICE*_HANDLER macros to
declare device callbacks with default mem_mask
parameters. [Aaron Giles]
