Expected impl:
    Before:
        [ A B C D E F G H I X ]
                          ^
                          |
                         TOS = top of stack, the last position w/ valid data

    tokdel(2, 7)
        [ A B C D E F G H I X ]
              ^ ^ ^ ^ ^ ^
              | | | | | |
      beg -- ´ \| | | |/`----- end
                \ | | /
                 \| |/
                  \ /
                   |
                 delete!

    After:
        [ A B I ? ? ? ? ? ? X ]
              ^
              |
             TOS
                 


Old impl:
    Before:
        [ A B C D E F G H I X ]
                          ^ TOS

    tokdel(2, 7)
        [ A B C D E F G H I * ]
              ^           ^
              |           `- token_stack + end + 1 <-- move from here
              |
               `------------ token_stack + beg     <-- to here 

                             end - beg + 1 = 6     <-- this amount of data

    Thus, these positions will be moved: 
        [ A B C D E F G H I X ? ? ? ? ? ? ? ]
                          ^ ^ ^ ^ ^ ^
    After:
        [ A B I * ? ? ? ? I X ]
              ^ TOS

    The stack is still valid, but we have accidentally copied data from outside
	of the token stack (the `?' positions)


New impl:
    Before:
        [ A B C D E F G H I X  ]
                          ^ TOS

    tokdel(2, 7)
        [ A B C D E F G H I X ]
              ^           ^
              |           `- token_stack + end + 1 <-- move from here
              |
               `---------- token_stack + beg       <-- to here 

              tos - 1 - end = 1                        <-- this amount of data

    Thus, we only move:
        [ A B C D E F G H I X ]
                          ^ TOS
                          `- token_stack + end + 1 <-- move from here

                             tos - end = 1         <-- this amount of data

    After:
        [ A B I D E F G H I X ]
              ^ TOS

    Valid stack, less copied data, no accesses outside of the token stack

In the actual code, the variable `tos' actually points to the first unused 
position of the stack (or the next position to put data onto, if you will) 
so in the patch, `tos - end - 1' is used as size for the memmove call.