GXemul Code2

MIPS zr register is now read-only, the MIPS "model" variable can be changed (and m_type is internally updated correctly).

Beginning on variable write handlers.

Merging in HISTORY file entries from the C++ branch into the main HISTORY file, for preservation.

Partial support for choosing MIPS ABI (affects disassembly and register dumps, mostly).

Separating out the dyntrans specific parts of CPUComponent into another base class, CPUDyntransComponent, so that it in theory is possible to implement non-dyntrans CPUs.

Getting rid of the last 'delete' call (in MainbusComponent,
there was a _pointer_ to a memory map, instead of just a
memory map). The new GXemul framework is thus completely free
of malloc/free and manual delete. (mmap/munmap are, for natural
reasons, used though by the RAMComponent.)

Avoid warnings with old GNU C++.

Use the ptrdiff directly.

20090804 Using anonymous unions and ptrdiff_t, to avoid overloading
pointers and size_t members unsafely, and other size_t usage.
(Thanks to Weinholt for commenting on this.)

Beginning on M88K bsr and jmp.n instruction implementations, and function call trace support.