INT 88 - APL*PLUS/PC - DETERMINE NAME STATUS
        AL = F9h
        ES:SI -> name
        CX = length of name
Return: CF set if name ill-formed or already in use
            BX = STPTR if already in symbol table
        CF clear if name is available for use
            BX = 0000h
Note:   does not force the name into the workspace
SeeAlso: AL=FEh,AL=FFh,INT C8"APL"