GLOCs are going away.

[Marius Vollmer]

Hi,

here is what I plan to do in the near future, just so that you know.

    - find a tc7 tag for variables so that they are more quickly to
      identify.

    - change the evaluator so that evaluating a variable yields its
      value (setting it sets its value).

    - memoize global symbols not to glocs but to variables.

    - remove all code pertaining to glocs.

    - remove the vcell-slot-hack from structures and the klugy code to
      tell structures from glocs.

    - think about the tags of structures and maybe clean them up as
      well (that is, find them a proper tc3 tag, if they don't already
      have one).

This oughta cleanup the tagging landscape of Guile and, mor
importantly, remove or at least lessen the special status of memoized
code.  The goal is to turn memoized code into a proper Scheme data
structure that can be manipulated confidently and without tricks.