Always "make clean" for lisp files before compiling them

	* Makefile: prepend "make clean" in lisp directory when compiling

Rationale: Emacs prefers the compiled lisp files even if the source is newer.
In case of circular dependencies or if the dependencies file is not correct,
the compiled files might not reflect the sources.  Since there is no canonical
way to remove all compiled files which are stale (it can be hacked, but it is
really ugly), it seems more prudent to just always remove the compiled files
before starting the compilation.  Most folks already already do that anyway.

targets.mk

@@ -12,6 +12,7 @@ INSTSUB         = $(SUBDIRS:%=install-%)
 	autoloads cleanall clean cleancontrib cleanelc cleandoc cleanrel
 
 compile:	lisp
+	$(MAKE) -C $< clean
 	$(MAKE) -C $< $@
 
 all \