Int 21 Fn 2513  P - Phar Lap 386/dos-extender - Alias Segment Descriptor   [E]

   AX = 2513h
   BX = segment selector of descriptor in GDT or LDT
   CL = access-rights byte for alias descriptor
   CH = use-type bit (USE16 or USE32) for alias descriptor

Return: CF clear if successful
       AX = segment selector for created alias
   CF set on error
       EAX = error code
       08h insufficient memory (can't grow LDT)
       09h invalid segment selector in BX