Applied the mainline PCem slight CPU emulation speedup commit;
Added emulation of removable SCSI hard disks;
CD-ROM image handler now uses C FILE's (with the 64-bit size calls) instead of C++ iostreams, ISO images bigger than 2 GB should work properly again;
Split RLL/ESDI and XT IDE disks to their own bus types;
Turned status bar pane meaning and hard disks and CD-ROM BUS numbers to #define's;
Other miscellaneous cleanups.
