Allocate Specific LDT Descriptor


                 This function attempts to allocate a specific LDT
                 descriptor.

            To Call

                 AX = 000Dh
                 BX = Selector

            Returns

                 If function was successful:
                 Carry flag is clear.
                 Descriptor has been allocated

                 If function was not successful:
                 Carry flag is set.

            Programmer's Notes

                 o    This function  will fail if the selector specified
                      in BX is in use or is not an LDT selector.
                 o    Use function 0001h to free the descriptor.
                 o    The first  10h (16  decimal) descriptors  must  be
                      reserved for  this function and may not be used by
                      the host.
                 o    If another  application has  already  loaded  then
                      some of these descriptors may be in use.