Use AMOP representation of canonicalized default initargs for conditions

Use AMOP representation of canonicalized default initargs for conditions

This fixes two issues:

1. CLASS-DIRECT-DEFAULT-INITARGS did not work for condition
   classes (bug 1164970)

2. Constant functions as default initargs of condition classes did not
   work correctly (bug 539517)

The following things have been changed:

* CONDITION-CLASSOID-DEFAULT-INITARGS is now called
  CONDITION-CLASSOID-DIRECT-DEFAULT-INITARGS to better reflect its
  purpose.

* Previously, default initargs of condition classes where stored in a
  plist the values of which where constant initforms or
  initfunctions. Now default initargs of condition classes are always
  of the form

    (INITARG INITFORM THUNK)

  as described in AMOP.

* The SHARED-INITIALIZED :AFTER CONDITION-CLASS T method now stores
  the direct default initargs in the class plist. These are now of the
  correct form as described in the previous bullet point.

* The DOPLIST macro used to be defined in src/pcl/macros.lisp. It is
  now in src/code/early-extensions.lisp and exported from SB-INT. This
  was necessary to use DOPLIST in src/code/condition.lisp.

* Unit test for both problems have been added.

fixes lp#539517, fixes lp#1164970