POP-STACK-DOWN

Equivalent to pulling a paper cup out of one of those dispensers they have on airplanes. The current (bottom) spectrum is lost, and all other spectra move down one position.

Examples:

    Stack posn    Scan no    Title
        X            4      doc                       
        Y            3      grumpy                    
        Z            2      sneezy                    
        T            1      dopey                     

    >> pop-stack-down <CR>
    X-register now contains scan    3: grumpy
    Number of stack positions in use is  3
    ..

    >> show-stack <CR>
    Number of stack positions in use is  3

              Data stack contents

    Stack posn    Scan no    Title
        X            3      grumpy                    
        Y            2      sneezy                    
        Z            1      dopey                     
        T