GXemul Code2

Adding 'R' (upper-case) disk image prefix, as a shorthand for creating temporary overlays.

Adding unlikely(), although it is unlikely that it matters that much.

Beginning to experiment with detecting/implementing support for the idle function used by OpenBSD/luna88k.

Adding hardcoded boot_unit=0 and boot_partition=0 NVRAM variables to the LUNA-88K machine, allowing OpenBSD/luna88k to boot from disk without asking for root and swap partitions.

Some color in the usage message and other messages.

Minor debugmsg:ification of diskimage messages, including minor improvement regarding r: prefix.

Reset to normal at end of line, even when not showing decorations.

Allow bootarg to be set to an empty string; needed for booting Sprite when using config files.

Minor src/net/README update.

Applying a patch from George Matsumura to make things build better on Linux: __attribute__((__packed__)); in bootblock.h.