Changed the makefile targets to use ${FASL} and ${CFASL} as the file

extensions.  The makefile now sets the value of FASL and CFASL at the
beginning to the correct extensions for the given target lisp.
Also, compile-file no longer uses :output-file to force
the fasls to have .fasl extensions.  This means that the lisp
implementation can write fasl's with whatever extension it wants and
the makefile will still work.
Made fasl-nodes, cfasl-nodes, and source-file-nodes have a
source-filepath slot.  This is now used in the asd-generator instead
of target.