Excluded component accessor-defgenerics from phase 1.

This is the beginning of an attempt to eliminate this file all
together.  Its sole purpose at the moment is to facilitate the
implementation of ENSURE-GENERIC-FUNCTION and DEFGENERIC later in the
bootstrapping process, and to avoid compiler warnings in phase 1.  But
it is redundant, so it creates a maintenance problem.  The goal is to
have a single definition of DEFGENERIC, and to redefine
ENSURE-GENERIC-FUNCTION as needed.
Rearranged class definitions.

It is important to order the class definitions in this file
depth-first pre-order, because that is how the classes will eventually
be finalized.  Since finalization is where unique class numbers are
assigned, this order ensures that a subtree of classes have
consecutive class numbers, thus making dispatch faster.

The result of this rearrangement is a depth-first pre-order as before,
except that now, the definition of BUILT-IN-CLASS comes AFTER the
definition of the subtree with REGULAR-CLASS as its root.  The reason
for this rearrangement is that the subtree with REGULAR-CLASS as its
root has some accessors for which we have DEFMETHOD forms spacialized
to BUILT-IN-CLASS, and this rearrangement ensures that the
corresponding generic functions are created when the DEFMETHOD forms
are seen, thus avoiding warnings from the compiler.