Prepare for pre-loading the call history of some generic functions.

Normally, the call history of a generic function is computed lazily.
However, there are two cases where it is advantageous to load the call
history of a generic function before it has been called the first
time:

  * The first and most important case is for specified generic
    functions with potential metastability issues.  For instance, we
    do not want the generic function COMPUTE-DISCRIMINATING-FUNCTION
    to call COMPUTE-DISCRIMINATING-FUNCTION in order to compute a
    discriminating function for itself.  By making sure there is
    already an effective method for that particular case, we avoid the
    metastability problem.

  * The second, less important case (because it could be solved
    differently in many ways) is during bootstrapping when some
    generic functions are host generic functions and others are bridge
    generic functions.  By making sure that all specified generic
    functions have full call-histories when defined as bridge generic
    functions, we avoid having any of them make calls to generic
    functions that need to be host generic functions in order for
    things to work, whereas they have been replaced by bridge generic
    functions.