Changes to ease code compilation in GCC.
Disk_t and HDD contain a std::string and for this reason they need a proper constructor, ZeroMemory is not guaranteed to work.
1) Uthernet card now returns floating bus for slot ROM at $Cs00-CsFF (where s=3).
2) Fixed IoHandlerCardsIn() to not map in the card in slot3's slot ROM when SLOTC3ROM=0.
Also:
. moved the typedef 'iofunction' from common.h to memory.h