ExoFreeSelector()  Cancels a protected mode segment descriptor
 ExoIsDPMI()        Determines if running in a DPMI host environment
 ExoIsExoSpace()    Determines if running under CA-Clipper/Exospace
 ExoIsPM()          Determines if the CPU is running in protected mode
 ExoIsVMM()         Determines if CA-Clipper/Exospace VMM system is in use
 ExoProtectedPtr()  Creates a protected mode pointer from a real mode pointer
 ExoRealPtr()       Creates a real mode pointer from a protected mode pointer
 ExoReside()        Flags a VMM segment to remain resident in memory
 ExoRMInterrupt()   Sets the registers, then signals a real mode interrupt
 ExoSegCSAlias()    Creates a code descriptor for the given data segment
 ExoSegDSAlias()    Creates a data descriptor for the given code segment
 _xalloclow()       Allocates low DOS memory for use with real mode interrupts
 _xfreelow()        Frees memory allocated by _xalloclow()