Better fixes for conflicts with SBBS3 headers/source... there are still a

couple outstanding issues however:

bstrlen()
- behaviour is different for control keys (xsdk doesn't count them)
DCD
- Conflicts with riodefs.h (different values)
SYSOP
- Conflicts with sbbsdefs.h (different variable names)
SAVELINE
- Conflicts with sbbsdefs.h (utterly different - xsdkdefs.h wrong?)
RESTORELINE
- Conflicts with sbbsdefs.h (utterly different - xsdkdefs.h wrong?)