Change all RTL constructs that contain pointers to compiler internal

Change all RTL constructs that contain pointers to compiler internal
data structures so that they only point to symbolic structures.  This
means that all occurrences of continuation and procedure objects have
been replaced by the corresponding label.  There is now a fairly fast
map from the labels to their objects.

This was done to make it possible to change the debugging file output
routines so that they fasdump rather than writing their output.